CL05 SC11 AIR & WATER

by

Air and Water (Class 5 Science – Chapter 11)

1. The Hook (The Mystery & Discovery)

A. Did you know… that right now you are living at the bottom of an invisible ocean of gas called the atmosphere that stretches 10,000 km into space and exerts constant, unseen air pressure on everything around you?

B. Imagine if… you held a glass of water upside down with just a thin piece of cardboard underneath, and the water didn’t spill out at all! This happens because invisible moving air molecules crash into the cardboard from below, exerting a upward force powerful enough to keep the water glued inside the tumbler.

C. Did you know… that every time you sip juice through a straw, use a syringe, or fill an ink dropper, you are using the exact same physical principle that inflates aircraft tyres and keeps giant planes rolling down the runway? By reducing the air pressure inside the straw, the higher external atmospheric pressure pushes the liquid upward.

D. Imagine if… planet Earth had no ozone layer in the stratosphere. Without this crucial protective shield, harmful ultraviolet rays from the Sun would scorch the Earth’s surface, making life impossible. Furthermore, in the mesosphere (extending up to 85 km), incoming meteors and space rocks burn up upon entry, shielding our world from cosmic collisions every single day.

E. Did you know… that although three-fourths (3/4) of the Earth’s surface is covered with water, only a tiny fraction of it is fit for human use? Before liquid reaches your kitchen tap, municipal authorities must execute a multi-stage water purification process involving sedimentation, chemical treatment, multi-layer filtration through sand, gravel, and charcoal, and chlorination to destroy deadly bacteria.

2. Real-World Lesson (Why This Matters)

Understanding the properties of air and water is not merely an academic exercise—it forms the technological foundation of modern society, environmental protection, public health, and civil infrastructure:

  • Aerospace and Transportation Technology: The structural design of bicycles, automobiles, heavy trucks, and commercial aircraft relies directly on compressed air pressure in tyres to support massive structural loads. Additionally, understanding atmospheric layers allows commercial jets to cruise smoothly in the stratosphere (up to 50 km) above storm systems, while space agencies launch artificial satellites into the thermosphere (600 km) and exosphere (10,000 km) for global communication, GPS navigation, and climate monitoring.
  • Public Health and Municipal Sanitation: Access to clean drinking water prevents lethal waterborne epidemics. Municipal governments deploy industrial-scale water treatment works that mimic natural physical processes—utilizing chemical-assisted sedimentation, multi-tier bed filtration (coal, sand, gravel), and chemical chlorination—to process millions of liters of raw river water daily for urban populations.
  • Medicine and Healthcare Infrastructure: The precise mechanics of syringes, eye droppers, and pharmaceutical manufacturing rely on vacuum suction, differential air pressure, and distilled water. Distilled water, created through complete thermal evaporation and condensation, provides the chemically pure solvent required for intravenous medications, medical laboratory testing, and industrial batteries.
  • Global Climate Security and Environmental Action: The atmosphere acts as a global thermal regulator—stopping excessive solar heat from reaching the ground by day and trapping radiating warmth at night. Understanding the function of the ozone layer in the stratosphere drives international environmental policies (such as combatting the ozone hole), while local water conservation practices (e.g., harvesting AC condensate, fixing pipeline leaks) ensure resource sustainability in drought-prone regions.

3. Activities

In-Class Experiments (From the Textbook)

  1. Combustion Dependency Experiment (Let’s Do – 1):
    • Objective: Prove that oxygen in the air is essential for burning.
    • Materials: Two identical candles, a matchbox, a clear glass tumbler.
    • Procedure: Light both candles on a flat surface. Invert the glass tumbler over one candle while leaving the second candle uncovered.
    • Observation: The covered candle extinguishes after a few seconds as the trapped oxygen is consumed, while the uncovered candle continues burning continuously.
  2. Downward and Upward Air Pressure Demonstration (Let’s Do – 2):
    • Objective: Demonstrate that air exerts upward pressure.
    • Materials: A glass tumbler, water, a piece of thick cardboard.
    • Procedure: Fill the glass completely to the brim with water, ensuring zero air bubbles remain. Press the cardboard firmly over the rim. Invert the glass upside down while holding the cardboard, then gently release your hand from the card.
    • Observation: The cardboard remains sealed against the glass brim and the water does not pour out, held in place by the upward atmospheric pressure.
  3. Soluble Impurity Extraction via Thermal Evaporation (Let’s Do – 3):
    • Objective: Extract dissolved soluble impurities (salt) from water.
    • Materials: 5–10 tablespoons of table salt, water, a shallow pan, a gas stove.
    • Procedure: Dissolve the salt thoroughly in water to prepare a concentrated salt solution. Heat the pan over the stove until all liquid boils away as water vapour.
    • Observation: White salt crystals remain behind on the bottom of the pan, demonstrating that evaporation separates soluble solids from liquids.

Experiential & Hands-On Activities (Supplementary Learning)

  1. Interactive Straw-Suction & Syringe Lab:
    • Provide students with juice cups, drinking straws, and medicine syringes without needles. Have them observe how liquid moves up only when internal air pressure is reduced by suction or pulling the syringe plunger backward.
  2. Construct a Mini Filtration Column:
    • Cut a plastic bottle in half, invert the top neck downward into the base, and layer it from bottom to top with cotton, activated charcoal, fine sand, and coarse gravel. Pass muddy water through it to visually observe how multi-stage filtration removes suspended particles.
  3. Municipal Water Plant Role-Play & Flow Simulation:
    • Assign students roles as River Reservoir, Sedimentation Tank, Sand-Gravel Filter, Chlorination Unit, and Household Tap. Pass colored counters representing dirt particles and bacteria along the line, physically removing them at each station to understand civil water supply infrastructure.
  4. “Be Water Smart” Water Audit:
    • Have students conduct a 24-hour home audit using the textbook checklist: tracking bucket baths vs. showers, checking for leaking faucets, placing ice cubes on house plants, and collecting AC condensate for cleaning.

4. Diagrams & Maps

To master the chapter visually, students should draw, label, and explain the following core scientific diagrams:

  1. Combustion Setup (Oxygen Requirement):
    • Illustration: Two lighted candles on a table; one covered with an inverted glass tumbler.
    • Required Labels: Burning candle, Inverted glass tumbler, Candle stops burning (extinguished).
    • Explanation: Shows that fire requires a continuous supply of oxygen present in atmospheric air.
  2. Air Pressure Cardboard Tumbler Setup:
    • Illustration: An inverted glass tumbler filled with water, held upside down with a flat cardboard underneath.
    • Required Labels: Glass tumbler filled with water, Thick cardboard, Upward Air Pressure arrow.
    • Explanation: Proves air molecules exert force in all directions, including upward pressure against gravity.
  3. Composition of Air (Pie Chart):
    • Illustration: A circular pie chart divided into proportionate sector angles.
    • Required Labels: Nitrogen (78%), Oxygen (21%), Argon, Carbon Dioxide and Other Gases (1%).
    • Explanation: Visualizes the gas proportions forming Earth’s atmosphere.
  4. Layers of the Atmosphere Diagram:
    • Illustration: Concentric atmospheric cross-section rising from Earth’s crust upward.
    • Required Labels & Altitude Markers:
      • Troposphere (0 to 15 km) – Weather changes, clouds, breathable air.
      • Stratosphere (15 km to 50 km) – Aircraft cruising zone, Ozone Layer.
      • Mesosphere (50 km to 85 km) – Burning meteors.
      • Thermosphere (85 km to 600 km) – High temperatures (500°C–2000°C+), artificial satellites.
      • Exosphere (600 km to 10,000 km) – Thinnest outer boundary, satellites, deep space transition.
  5. Sedimentation and Decantation Apparatus:
    • Illustration: Two sequential beaker setups.
    • Required Labels: Mixture of sand and water, Sediments of sand, Glass rod, Clear water.
    • Explanation: Demonstrates gravity settling of heavy insoluble solids followed by gentle pouring of clear supernatant liquid.
  6. Filtration Cone Apparatus:
    • Illustration: Conical folded filter paper fitted inside a glass funnel placed over a conical flask.
    • Required Labels: Mixture of chalk powder and water, Filter paper (folded cone), Funnel, Flask, Clear water (filtrate).
    • Explanation: Illustrates physical straining of insoluble suspended solids through microscopic paper pores.
  7. Laboratory Distillation Unit:
    • Illustration: Complete thermal purification rig mounted on stands.
    • Required Labels: Tripod stand, Gas burner, Round-bottom Distillation flask, Mixture of salt and water, Thermometer, Clamp stand, Condenser (cooling sleeve), Beaker, Pure Distilled Water.
    • Explanation: Shows boiling, vapor condensation back into liquid, and isolation of pure water from non-volatile impurities.
  8. Journey of Water to Our Homes (Flow Chart Map):
    • Illustration: Municipal waterworks sequence map from source to tap.
    • Required Labels: Water Reservoir / River \(\rightarrow\) Sedimentation Tank (Chemical Addition & Sludge Separation) \(\rightarrow\) Filtration Bed (Coal, Sand, Gravel) \(\rightarrow\) Chlorination & Fluoridation Tank \(\rightarrow\) Service Reservoir / Overhead Storage Tank \(\rightarrow\) Household Water Supply.

5. The Exhaustive Sequence / Process / Timeline

Process A: The Mechanics of Air Pressure Operations

  1. Molecules in the air are in constant random motion in all directions.
  2. When moving air encounters a surface, the colliding molecules exert physical force, termed air pressure.
  3. Application 1 (Drinking Straw): Inserting a straw into liquid establishes equal pressure inside and outside the tube. Sucking removes air from inside the straw, lowering internal internal pressure. The higher ambient atmospheric pressure pressing down on the liquid surface outside forces liquid up into the straw and mouth.
  4. Application 2 (Inflatable Structures & Tyres): Pumping air forces gas molecules into a sealed volume (balloon/tyre). The molecules impact inner container walls, inflating it. Compressed air inside heavy vehicle tyres supports the full weight of trucks and airplanes.

Process B: Thermal & Physical Removal of Insoluble Water Impurities

  1. Sedimentation Step: Insoluble heavy particles (e.g., sand, mud) mixed in water are allowed to stand undisturbed in a container. Gravitational pull draws denser particles downward to form a bottom layer called sediment.
  2. Decantation Step: The upper layer of clarified water is carefully poured off into a secondary vessel along a glass rod without disturbing the settled sediment at the bottom.
  3. Filtration Step: For lighter suspended particles (e.g., chalk powder):
    • A circular filter paper is folded twice into quarters and opened into a cone shape.
    • The cone is inserted inside a glass funnel positioned above a collection flask.
    • The turbid liquid is poured onto the filter cone. Clean liquid (filtrate) passes through fine pores into the flask, while insoluble residue remains trapped on the paper.

Process C: Removal of Soluble Impurities & Production of Distilled Water

  1. Boiling/Simple Evaporation: Heating a solution of soluble impurities (e.g., salt water) causes liquid \(\text{H}_2\text{O}\) to absorb thermal energy and transform into water vapour, escaping into the atmosphere and leaving solid dry solute behind.
  2. Distillation Engine:
    • Impure water containing dissolved solids is poured into a round-bottom distillation flask mounted on a tripod stand over a heat source.
    • As temperature rises (monitored by a top-mounted thermometer), liquid water reaches its boiling point and turns into vapour. Non-volatile soluble impurities remain at the bottom of the flask.
    • Hot water vapour enters a side tube connected to a liquid-cooled condenser.
    • Thermal transfer inside the condenser cools the vapour, causing gas to condense back into liquid water.
    • Purified liquid streams out of the condenser into a receiving beaker as distilled water.

Process D: Municipal Water Supply Engine

  1. Raw Water Extraction: Surface water is pumped from rivers or reservoirs into the municipal treatment plant.
  2. Chemical-Assisted Sedimentation: Water enters large settling basins where specific coagulating chemicals are added to clump fine suspended dirt into heavy sludge, which sinks to the bottom.
  3. Multi-Bed Filtration: Clarified water flows through deep filtration beds layered sequentially with coal/charcoal, sand, and gravel to strain out microscopic suspended solids and large impurities.
  4. Disinfection (Chlorination & Fluoridation): Filtered water passes into chlorination tanks where controlled quantities of chlorine gas/compounds are added to destroy pathogenic bacteria causing waterborne diseases.
  5. Storage & Distribution: Purified water is pumped into elevated service reservoirs (overhead tanks) and distributed through municipal pipe networks to city households.
  6. Point-of-Use Safety: Because distribution pipes can harbor leaks or secondary contamination, water should be boiled or passed through domestic filtration filters prior to consumption.

6. Comprehensive Vocabulary (The Word List)

  1. Air – A colourless, tasteless, and odorless mixture of gases surrounding the Earth – Used in this chapter as the primary atmospheric fluid required for respiration, combustion, and pressure generation.
  2. Wind – Air that is in horizontal or active motion – Referenced in the chapter as the tangible, feelable state of moving air.
  3. Photosynthesis – The biological process by which green plants utilize carbon dioxide, water, and sunlight to make food – Mentioned as the process for which plants absorb carbon dioxide from air.
  4. Combustion (Burning) – A chemical reaction between a fuel and oxygen that releases heat and light energy – Used in the candle experiment to prove oxygen is essential for fire.
  5. Air Pressure – The physical force exerted on a unit area of surface by the weight and movement of air molecules – Highlighted as the operational force behind drinking straws, syringes, droppers, and vehicle tyres.
  6. Atmosphere – The protective blanket of air held around the Earth by its gravitational pull – Defined as the five-layered envelope of gas surrounding the planet.
  7. Ozone Layer – A specialized region within the stratosphere containing high concentrations of ozone gas (\(\text{O}_3\)) – Contextualized as the thermal and radiation filter that blocks destructive solar ultraviolet rays.
  8. Ozone Hole – A depleted, thinned area in the ozone layer caused by atmospheric pollution – Referenced in the Discover and Learn section as a topic of environmental study.
  9. Troposphere – The lowest layer of Earth’s atmosphere extending from sea level up to 15 km – Described as the weather-active zone containing breathable air and cloud formations.
  10. Stratosphere – The second atmospheric layer extending from 15 km up to 50 km above Earth – Highlighted as the smooth flying zone for commercial aircraft and host to the protective ozone layer.
  11. Mesosphere – The middle atmospheric layer extending from 50 km up to 85 km – Contextualized as the cosmic shield where meteors and rock fragments burn up upon entry.
  12. Thermosphere – The fourth atmospheric layer extending from 85 km up to 600 km – Characterized by extreme temperature ranges (500°C to 2000°C+) and hosting orbiting artificial satellites.
  13. Exosphere – The uppermost and thinnest layer extending up to 10,000 km – Referenced as the outermost atmospheric boundary where air thins into outer space and satellites orbit.
  14. Baayumondol (বায়ুমণ্ডল) – The Bengali word for Earth’s atmosphere – Introduced in the language learning section.
  15. Valimantalam (வளிமண்டலம்) – The Tamil word for Earth’s atmosphere – Introduced in the language learning section.
  16. Impurities – Unwanted, harmful, or dirty foreign substances (mud, sand, twigs, germs) that render water unsafe – Defined as the primary target of physical and chemical purification methods.
  17. Soluble Impurities – Foreign substances that completely dissolve in water (e.g., salt) forming a clear liquid solution – Referenced in connection with evaporation and distillation purification.
  18. Insoluble Impurities – Indissoluble solid particles (e.g., sand, chalk powder, twigs) that remain suspended or settle in water – Addressed using physical separation methods like sedimentation, decantation, and filtration.
  19. Sedimentation – The physical settling process where insoluble heavy particles sink to the bottom of an undisturbed liquid – Described as the initial stage of solid-liquid gravity separation.
  20. Sediment – The accumulated layer of solid insoluble particles that settles at the bottom of a liquid vessel – Identified as the settled layer (e.g., sand) left after sedimentation.
  21. Decantation – The careful pouring off of top clear liquid without disturbing lower settled sediment – Defined as the complementary follow-up process to sedimentation.
  22. Filtration – The process of passing dirty liquid through a porous barrier (like filter paper) to separate suspended solids – Contextualized through laboratory funnel activities and municipal sand-charcoal beds.
  23. Filtrate / Clear Water – The purified liquid collected in the receiving vessel after passing through a filter barrier – Identified as the clear fluid output in the chalk-water filtration experiment.
  24. Evaporation – The phase transition process where liquid water converts into gaseous water vapour upon absorbing heat – Used to isolate dissolved soluble solids like salt from sea water.
  25. Distillation – A double phase-change purification process comprising thermal vaporization of liquid followed by vapor condensation – Defined as the process yielding pure distilled water.
  26. Condenser – A laboratory apparatus tube designed to cool hot vapor back into liquid form during distillation – Identified as the cooling jacket apparatus in the distillation assembly.
  27. Distilled Water – Ultra-pure water completely free of dissolved solids, minerals, and microorganisms obtained via distillation – Specified for use in automobile batteries, scientific labs, and pharmaceutical industries.
  28. Chlorination – The chemical application of chlorine compound gas to water supplies – Contextualized as the disinfection step in municipal waterworks to destroy pathogenic bacteria.
  29. Fluoridation – The added chemical treatment stage during municipal processing to support public health – Listed alongside chlorination in municipal supply flowcharts.
  30. Sludge – The dense accumulated chemical and organic sediment precipitated during municipal water sedimentation – Identified in the municipal purification flow diagram.

7. Teacher’s Chapter Checklist

Teachers can use this instructional checklist to track target competencies and mapping across the chapter:

  • [ ] Core Air Concepts & Properties:
    • [ ] Can define air, wind, and basic gaseous properties.
    • [ ] Can explain essential biological uses: Oxygen for respiration/combustion, Carbon Dioxide for photosynthesis.
    • [ ] Can execute and explain Experiment 1 (Candle Combustion under inverted glass).
    • [ ] Can verify properties: Air occupies space, air has mass, air exerts pressure in all directions.
    • [ ] Can execute and explain Experiment 2 (Inverted cardboard tumbler holding water).
    • [ ] Can detail practical applications of air pressure: drinking straws, syringes, eye/ink droppers, balloons, tyres/aircraft.
  • [ ] Atmospheric Structure & Composition:
    • [ ] Knows exact volumetric gas proportions: 78% Nitrogen, 21% Oxygen, 1% Other Gases (\(\text{CO}_2\), Argon, Helium, Neon, Hydrogen, Ozone).
    • [ ] Defines atmosphere and explains gravity’s role in air density.
    • [ ] Details functions of atmosphere: ozone layer radiation protection, day/night temperature maintenance.
    • [ ] Can list, order, and describe all 5 atmospheric layers with exact altitude boundaries and key features:
      • [ ] Troposphere: Up to 15 km; cloud formation, weather changes, breathable air.
      • [ ] Stratosphere: Up to 50 km; commercial aircraft flight path, ozone layer location.
      • [ ] Mesosphere: Up to 85 km; meteor burning shield.
      • [ ] Thermosphere: Up to 600 km; 500°C to 2000°C+ thermal range, satellite orbits.
      • [ ] Exosphere: Up to 10,000 km; thinnest outer boundary, space transition, satellites.
    • [ ] Cross-cultural vocabulary awareness: Baayumondol (Bengali), Valimantalam (Tamil).
  • [ ] Water Properties, Impurities & Separation Mechanics:
    • [ ] Identifies Earth surface coverage proportion (3/4) and key water sources.
    • [ ] Distinguishes clearly between Soluble (e.g., salt) and Insoluble (e.g., sand, twigs, chalk) impurities.
    • [ ] Demonstrates understanding of insoluble impurity removal:
      • [ ] Sedimentation & Decantation: Gravity settling and pour-off mechanics.
      • [ ] Filtration: Funnel cone folding, porous paper barrier, residue vs filtrate separation.
    • [ ] Demonstrates understanding of soluble impurity removal:
      • [ ] Boiling / Evaporation: Thermal salt extraction (Experiment 3).
      • [ ] Distillation: Flask heating, condenser cooling, distilled water collection.
    • [ ] Identifies 3 specific industrial uses of distilled water: batteries, science labs, pharmaceutical industries.
  • [ ] Civil Supply & Conservation:
    • [ ] Maps out the 4 sequential stages of municipal water purification: Sedimentation (Chemical addition) \(\rightarrow\) Filtration (Coal, Sand, Gravel) \(\rightarrow\) Chlorination & Fluoridation \(\rightarrow\) Storage Tanks.
    • [ ] Understands domestic re-contamination risks and post-tap boiling/filtering solutions.
    • [ ] Memorizes and applies 9 practical water conservation measures (“Be Water Smart”).

8. Ready-Reckoner Student Revision Notes

I. The Science of Air

A. Basic Characteristics

  • Air is a colourless, invisible mixture of gases surrounding the Earth.
  • Moving air is called wind.
  • All living organisms require oxygen in air for respiration, while green plants absorb carbon dioxide for photosynthesis.
  • Combustion Requirement: Oxygen is indispensable for fire. An inverted glass placed over a lit candle cuts off fresh air, extinguishing the flame once trapped oxygen is consumed.

B. Fundamental Properties of Air

  1. Air Occupies Space: An inflated balloon takes up significantly more space than a deflated balloon.
  2. Air Has Mass: An inflated balloon weighs more on a balance scale than a deflated balloon.
  3. Air Exerts Pressure:
    • Air molecules move constantly in all directions, exerting force on every surface they strike.
    • Cardboard-Glass Proof: Water filled to the brim in a tumbler is held inside when inverted over cardboard because upward atmospheric pressure pushes against the card from underneath.
    • Everyday Applications:
      • Drinking Straw: Sucking reduces internal straw pressure; higher external atmospheric pressure pushes liquid up into the mouth.
      • Medical/Lab Devices: Syringes, eye droppers, and ink droppers operate via differential pressure.
      • Inflatables & Travel: Compressed air inside tyres supports bicycles, cars, buses, heavy trucks, and aircraft.

II. Earth’s Atmosphere

A. Gas Composition

  • Nitrogen: \(78%\) (Largest component)
  • Oxygen: \(21%\) (Essential for life and burning)
  • Other Gases (\(1%\) Total): Carbon dioxide, Argon, Helium, Neon, Hydrogen, Ozone, etc.

B. Importance of Atmosphere

  • The atmosphere is a thin gaseous blanket pulled close to Earth by gravity.
  • Contains the Ozone Layer, which shields Earth by blocking harmful solar rays.
  • Regulates planet temperature: prevents excessive daytime heating and traps thermal heat at night.

C. The 5 Atmospheric Layers

Layer NameAltitude RangeCore Features & Events
Troposphere\(0 \text{ km}\) to \(15 \text{ km}\)First layer; contains breathable air and most clouds; all weather changes occur here.
Stratosphere\(15 \text{ km}\) to \(50 \text{ km}\)Jet aircraft fly smoothly here; hosts the protective Ozone Layer.
Mesosphere\(50 \text{ km}\) to \(85 \text{ km}\)Meteors and rock fragments burn up here, protecting Earth from impacts.
Thermosphere\(85 \text{ km}\) to \(600 \text{ km}\)Extremely hot (\(500^\circ\text{C}\) to \(2000^\circ\text{C}+\)); artificial satellites orbit here.
Exosphere\(600 \text{ km}\) to \(10,000 \text{ km}\)Thinnest outer layer; no air beyond this limit; satellites orbit here.

III. Water and Its Purification

A. Water Distribution & Impurity Types

  • Water covers three-fourths (\(3/4\)) of Earth’s surface, but very little is directly usable.
  • Major raw sources: Rivers, lakes, wells, underground reservoirs, rainwater.
  • Impurities are categorized into two classes:
    1. Insoluble Impurities: Solids that do not dissolve in water (e.g., sand, twigs, mud, chalk powder).
    2. Soluble Impurities: Substances that dissolve completely in water (e.g., salt).

B. Separation of Insoluble Impurities

  1. Sedimentation: Letting dirty water stand undisturbed so heavy solids settle to the bottom as sediment.
  2. Decantation: Pouring off the upper clear liquid into another glass without disturbing the settled sediment.
  3. Filtration: Pouring liquid through a cone of folded filter paper inside a funnel. Clean liquid passes through into the flask while suspended solids remain on the paper.

C. Separation of Soluble Impurities

  1. Boiling / Evaporation: Heating salt water causes liquid water to evaporate into steam, leaving pure salt crystals behind in the pan.
  2. Distillation:
    • Liquid is boiled in a round-bottom distillation flask.
    • Water steam rises and travels through a water-cooled tube called a condenser.
    • Steam cools down and condenses back into liquid water inside a receiving beaker.
    • Yields Distilled Water (the purest form of water).
    • 3 Major Uses of Distilled Water: Car/automobile batteries, scientific research laboratories, and pharmaceutical manufacturing.

IV. Municipal Water Supply & Conservation

A. Municipal Purification Stages

  1. Sedimentation Tank: Water from river/reservoir is mixed with chemicals to make fine dirt clump and settle into sludge.
  2. Filtration Beds: Water drains through layers of sand, gravel, and coal/charcoal to remove remaining suspended dirt.
  3. Chlorination Tank: Chlorine chemical is added to destroy illness-causing bacteria and germs.
  4. Storage & Home Supply: Disinfected water is stored in giant overhead tanks/service reservoirs and piped to city homes.
  • Home Protection: Boil or filter tap water at home to kill germs that enter through leaky pipes.

B. The 9 Rules of “Be Water Smart”

  1. Never leave taps running while brushing teeth, shaving, or washing dishes.
  2. Run washing machines only with full laundry loads.
  3. Water garden plants early in the morning or late at night to minimize evaporation loss.
  4. Bathe using buckets rather than running showers.
  5. Wash fruits and vegetables in a water bowl instead of under a running faucet.
  6. Use buckets to clean household floors, windows, and motor vehicles.
  7. Promptly inspect and repair leaking plumbing pipes.
  8. Place leftover ice cubes on house plant soil; reuse fruit/veg wash water for plants.
  9. Collect rainwater and air conditioner condensate for plant watering and vehicle washing.

QUESTIONS :

Master Question Bank: Class 5 Science Chapter 11 — Air and Water: Properties and Purification

1. The “Hidden” In-Text Questions (Mid-Chapter Extraction)

Section: Introduction, Warm-Up & “I Wonder”

Q1.1. What natural force pulls the blanket of air (atmosphere) closer to the surface of the Earth, making it thicker near the ground?

Q1.2. Based on the mid-chapter “I wonder” question, why can a human being survive for several days without food or water, but cannot survive for more than a few minutes without air?

Section: Air — Properties & Uses

Q1.3. Why does a covered candle extinguish in the “Let’s Do – 1” experiment while an uncovered candle continues to burn continuously?

Q1.4. How does an inflated balloon prove two fundamental physical properties of air simultaneously (that air has mass and occupies space)?

Q1.5. In the “Let’s Do – 2” experiment, what specific directional pressure prevents water from spilling out of an inverted glass covered with cardboard?

Q1.6. Explain the exact pressure differential created inside a straw when a person sucks air out of it to drink juice.

Q1.7. Name three common appliances or medical instruments mentioned in the text that operate on the exact same air pressure principle as a drinking straw.

Section: Composition & Layers of the Atmosphere

Q1.8. State the exact percentage breakdown of Nitrogen, Oxygen, and other rare gases in the atmosphere.

Q1.9. In which specific atmospheric layer do all weather changes occur and clouds form?

Q1.10. Why do commercial jet aircraft prefer flying in the stratosphere rather than the troposphere?

Q1.11. Describe the protective role played by the mesosphere when space debris or meteors enter Earth’s atmosphere.

Q1.12. What extreme temperature range exists in the thermosphere, and what human-made objects orbit in this layer?

Q1.13. What happens to air molecules in the exosphere as it extends up to 10,000 km into space?

Section: Language Integration Sidebar

Q1.14. Write the Bengali (Baayumondol) and Tamil (Valimantalam) translations for the word “Atmosphere” provided in the textbook sidebar.

Section: Water & Impurities

Q1.15. What fraction of the Earth’s surface is covered with water, and why is most of it not fit for direct human use?

Q1.16. Differentiate between soluble and insoluble water impurities based on their ability to dissolve in water, providing two examples of each from the text.

Section: Removal of Impurities (Insoluble & Soluble)

Q1.17. How does gravity assist in the sedimentation process of insoluble heavy particles like sand?

Q1.18. What precaution must be taken during decantation so that settled sediment is not transferred into the clean vessel?

Q1.19. Describe the physical geometry and arrangement of filter paper used inside a funnel during the filtration of chalk powder and water.

Q1.20. What thermal process is utilized on a large commercial scale to extract common salt from sea water?

Q1.21. Trace the two phase changes (state transitions) that water undergoes during the process of distillation inside a distillation flask and cooling condenser.

Q1.22. List three critical industrial and scientific applications where ultra-pure distilled water is mandatory.

Section: Journey of Water & Conservation

Q1.23. What specific chemical compound is added to municipal sedimentation tanks to help fine insoluble impurities clump together and settle?

Q1.24. Name the three distinct filtration layers (from bottom to top/bed composition) inside a municipal water treatment plant.

Q1.25. Why is chlorine gas or chemical chlorination introduced into filtered municipal water before distribution?

Q1.26. According to the “Be Water Smart” guide, how can household air conditioner (AC) condensate water be productively reused?

2. The Textbook Exercise Integration (Back-of-Chapter & In-Text)

Section A: In-Text “Warm-Up” & Introductory Questions

Q2.1. I wonder: How long can I stay without air?

Q2.2. Observe the chapter opening picture: Can you identify the use of water shown in the picture?

Q2.3. Can you list a few major water dam or river projects in India?

Section B: In-Text “Discover and Learn”

Q2.4. Rishi read somewhere about an ozone hole, but he cannot recollect what actually this hole is. Can you help him by writing briefly about it?

Section C: Mid-Chapter “Progress Check” (Textbook Assessment)

Instructions: Write T for True and F for False.

  1. Nitrogen present in the air is essential for burning purposes.
  2. The major part of the air composition is oxygen.
  3. The temperature in the thermosphere ranges from 500°C to 2000°C or higher.
  4. Mesosphere is the layer above the troposphere.
  5. Air has mass.

Section D: In-Text Activity Objectives (“Let’s Do”)

Q2.5. Let’s Do – 1 Aim: What is the objective of covering a burning candle with an inverted glass tumbler?

Q2.6. Let’s Do – 2 Objective: What property of moving air molecules is demonstrated using a glass tumbler, water, and thick cardboard?

Q2.7. Let’s Do – 3 Aim: How can you extract dissolved soluble salt from a prepared salt-water solution at home?

Section E: “Let’s Learn New Language”

Q2.8. Translate the English scientific term “Atmosphere” into:

  1. Bengali: ____________________
  2. Tamil: ____________________

3. Exhaustive Objective Bank (The Factual Baseline)

Multiple-Choice Questions (MCQs)

Q1. What percentage of the Earth’s atmosphere is composed of Nitrogen gas?

A) 21% B) 78% C) 1% D) 50%

Q2. Which atmospheric gas is essential for combustion (burning) and cellular respiration?

A) Nitrogen B) Carbon Dioxide C) Oxygen D) Argon

Q3. Which layer of the atmosphere extends from sea level up to 15 km?

A) Stratosphere B) Mesosphere C) Troposphere D) Thermosphere

Q4. In which layer of the atmosphere is the protective ozone layer located?

A) Troposphere B) Stratosphere C) Mesosphere D) Exosphere

Q5. What occurs in the mesosphere that prevents celestial objects from striking the Earth’s surface?

A) Artificial satellites orbit B) Weather changes occur C) Meteors and rock fragments burn up D) Jet aircraft fly smoothly

Q6. What is the temperature range in the thermosphere layer?

A) 0°C to 100°C B) -50°C to 0°C C) 500°C to 2000°C or higher D) 100°C to 500°C

Q7. Which atmospheric layer extends up to 10,000 km above the Earth and has no air beyond it?

A) Exosphere B) Thermosphere C) Stratosphere D) Mesosphere

Q8. What holds the thin blanket of air (atmosphere) close to the Earth’s surface?

A) Atmospheric pressure B) Earth’s gravity C) Solar energy D) Wind motion

Q9. What Bengali term is used for “Atmosphere” in the chapter’s language section?

A) Valimantalam B) Baayumondol C) Jalabondol D) Vayudoot

Q10. How much of the Earth’s surface is covered with water?

A) Half (1/2) B) One-fourth (1/4) C) Three-fourths (3/4) D) Two-thirds (2/3)

Q11. Which of the following is an example of a soluble impurity in water?

A) Sand B) Twigs C) Salt D) Chalk powder

Q12. What is the process called where insoluble impurities settle down at the bottom of an untouched liquid? A) Decantation B) Sedimentation C) Filtration D) Distillation

Q13. In the filtration method, what is the clear liquid collected in the flask called?

A) Sediment B) Residue C) Filtrate D) Solute

Q14. Which method is used to extract salt from sea water?

A) Filtration B) Decantation C) Evaporation D) Sedimentation

Q15. What is the purest form of water obtained by evaporating impure water and condensing its vapour?

A) Tap water B) Rainwater C) Distilled water D) Well water

Q16. Distilled water is widely used in which of the following applications?

A) Agricultural irrigation B) Automobile batteries C) Cooking food D) Swimming pools

Q17. What chemical is added to filtered municipal water to kill harmful bacteria?

A) Salt B) Chlorine C) Nitrogen D) Chalk

Q18. What substance is placed alongside sand and gravel in municipal filtration beds to strain insoluble impurities?

A) Salt B) Charcoal (Coal) C) Sugar D) Clay

Q19. When drinking juice through a straw, what causes the juice to rise into the mouth?

A) Increased air pressure inside the straw B) Higher atmospheric pressure outside the straw C) Gravity pushing the straw down D) Expansion of air inside the straw

Q20. What keeps a piece of cardboard glued to an inverted glass filled with water?

A) Gravitational pull downwards B) Upward air pressure pushing from below C) Suction from the glass top D) Friction between cardboard and glass

Q21. Why do commercial aircraft prefer flying in the stratosphere layer?

A) Meteors burn up in this layer B) Weather changes and clouds are absent here C) Satellites orbit in this layer D) Air density is highest here

Q22. Which gas forms 1% of the atmosphere along with argon, helium, neon, hydrogen, and ozone?

A) Nitrogen B) Oxygen C) Carbon dioxide D) Water vapour

Fill-in-the-Blanks

Q23. Moving air is known as ______.

Q24. Green plants take in ______ from the air for photosynthesis.

Q25. Air pressure is exerted because molecules of air are always in ______.

Q26. Compressed air filled in tyres supports vehicles like cars, buses, trucks, and ______.

Q27. The atmosphere consists of ______ nitrogen and ______ oxygen.

Q28. The ______ layer in the atmosphere prevents harmful rays of the sun from entering the Earth’s surface.

Q29. Weather changes take place in the ______ layer of the atmosphere.

Q30. Artificial satellites orbit the Earth in the ______ and exosphere layers.

Q31. In Tamil, the word for atmosphere is ______.

Q32. Impurities that do not dissolve in water are known as ______ impurities.

Q33. The process of pouring clear water into a separate container without disturbing the settled sediment is called ______.

Q34. In filtration, the filter paper is folded in the shape of a ______ and placed inside a funnel.

Q35. Distillation involves two consecutive physical processes: evaporation and ______.

Q36. In municipal water purification, water is pumped from the river into a tank where chemicals are added during the ______ stage.

Q37. According to the “Be Water Smart” guidelines, we should run our washing machines only with a ______ laundry load.

True/False Questions

(If False, correct the statement)

Q38. Nitrogen present in the air is essential for burning purposes.

Q39. Air has mass and occupies space.

Q40. The major part of the air composition is oxygen.

Q41. The temperature in the thermosphere ranges from 500°C to 2000°C or higher.

Q42. Mesosphere is the layer above the troposphere.

Q43. Sand and twigs are examples of soluble impurities in water.

Q44. Filtration can separate dissolved salt from water.

Q45. Distilled water is the purest form of water and is used in science laboratories and batteries.

Q46. In municipal water purification, chlorine is added to help insoluble impurities settle down.

Q47. Air pressure inside a drinking straw increases when you suck air out of it.

4. Subjective & Competency Bank (Higher-Order Thinking)

Short-Answer Questions

Q48. Explain why a candle covered with an inverted glass tumbler stops burning after a short time.

Q49. How does air pressure enable a syringe and an eye dropper to draw liquid upward?

Q50. Why is the atmosphere thicker near the surface of the Earth compared to higher altitudes?

Q51. Explain the primary function of the ozone layer present in the stratosphere.

Q52. How do meteors burning up in the mesosphere protect life on Earth?

Q53. Why is water drawn from rivers, lakes, and wells considered impure before treatment?

Q54. Explain the difference between soluble and insoluble impurities with one example of each.

Q55. How does decantation differ from sedimentation in the purification of water?

Q56. Why cannot simple filtration be used to separate dissolved salt from water?

Q57. Explain why tap water supplied to our homes may become contaminated even after municipal purification.

Scenario-Based / Competency Questions

Q58. Scenario 1: A group of mountaineers ascending a peak notices that it becomes harder to breathe as they go higher up the mountain. Based on the atmospheric properties discussed in the chapter, explain why air density decreases at higher altitudes.

Q59. Scenario 2: Rohan attempted to purify a mixture of salt, sand, and water using only filter paper and a funnel. He collected clear water in the flask, but when he tasted it, the water was still salty. Explain why filtration failed to remove the salt and describe what additional process Rohan must perform to get pure water.

Q60. Scenario 3: During a science exhibition, a student demonstrates an experiment where a glass filled with water and covered with cardboard is held upside down. A younger visitor claims the cardboard is sticking because of glue. How would you scientifically explain the mechanism to the visitor?

Q61. Scenario 4: A city’s municipal water treatment plant experienced a temporary supply shortage of chlorine gas. What immediate health risk does this pose to the city’s residents, and what two domestic precautions should households take before drinking the tap water?

Q62. Scenario 5: Priya wants to reduce water wastage at home. She notices her family leaving the tap running while brushing teeth and throwing unused ice cubes down the drain. Based on the “Be Water Smart” chapter guidelines, suggest 5 specific action steps Priya’s family can adopt.

Long-Answer / Essay Questions

Q63. Detail the complete operational mechanics of distillation, describing the function of every apparatus component (flask, burner, thermometer, condenser, receiver) and explaining why the resulting distilled water is indispensable in specific industries.

Q64. Compare and contrast all five layers of the atmosphere in terms of altitude range, temperature/air conditions, and unique natural phenomena or human activities occurring in each layer.

Q65. Describe the multi-stage journey of water from a river reservoir to a household tap as managed by municipal agencies, breaking down the specific physical and chemical processes executed at each stage.

Q66. Design a comparative study explaining the three major methods used to remove insoluble impurities (sedimentation, decantation, and filtration) and the two major methods used to remove soluble impurities (boiling/evaporation and distillation).

Q67. Explain the concept of air pressure in detail, supporting your answer with two laboratory experiments described in the text and three daily-life devices that function based on air pressure differentials.

5. The Master Answer Key & Marking Rubric

Answer Key: Objective Bank

MCQs

  • Q1: B) 78%
  • Q2: C) Oxygen
  • Q3: C) Troposphere
  • Q4: B) Stratosphere
  • Q5: C) Meteors and rock fragments burn up
  • Q6: C) 500°C to 2000°C or higher
  • Q7: A) Exosphere
  • Q8: B) Earth’s gravity
  • Q9: B) Baayumondol
  • Q10: C) Three-fourths (3/4)
  • Q11: C) Salt
  • Q12: B) Sedimentation
  • Q13: C) Filtrate
  • Q14: C) Evaporation
  • Q15: C) Distilled water
  • Q16: B) Automobile batteries
  • Q17: B) Chlorine
  • Q18: B) Charcoal (Coal)
  • Q19: B) Higher atmospheric pressure outside the straw
  • Q20: B) Upward air pressure pushing from below
  • Q21: B) Weather changes and clouds are absent here
  • Q22: C) Carbon dioxide

Fill-in-the-Blanks

  • Q23: wind
  • Q24: carbon dioxide
  • Q25: motion
  • Q26: aircraft
  • Q27: 78%, 21%
  • Q28: ozone
  • Q29: troposphere
  • Q30: thermosphere
  • Q31: Valimantalam
  • Q32: insoluble
  • Q33: decantation
  • Q34: cone
  • Q35: condensation
  • Q36: sedimentation
  • Q37: full

True/False (with Corrections)

  • Q38: False. Oxygen present in the air is essential for burning purposes (Nitrogen does not support burning).
  • Q39: True. Air occupies space and has mass.
  • Q40: False. The major part of the air composition is nitrogen (78%), while oxygen is 21%.
  • Q41: True. Temperature in the thermosphere ranges from 500°C to 2000°C or higher.
  • Q42: False. Stratosphere is the layer above the troposphere (Mesosphere is above the stratosphere).
  • Q43: False. Sand and twigs are examples of insoluble impurities in water.
  • Q44: False. Filtration cannot separate dissolved salt; evaporation or distillation is required.
  • Q45: True. Distilled water is ultra-pure water used in batteries, labs, and medicines.
  • Q46: False. Chlorine is added to kill harmful bacteria; specific coagulating chemicals are added during sedimentation to settle impurities.
  • Q47: False. Air pressure inside the straw decreases when air is sucked out, allowing higher ambient pressure to push liquid up.

Marking Rubrics: Subjective & Competency Questions

Short-Answer Questions Rubric

  • Q48 (Candle Experiment):
    • Required Points: Mentions that air contains a limited amount of oxygen inside the glass tumbler. State that once oxygen is consumed by combustion, the flame extinguishes.
    • Source Reference: Section: “Air”, Passage.
  • Q49 (Syringe & Dropper Mechanics):
    • Required Points: Explains that pulling the plunger/squeezing the bulb decreases internal pressure inside the chamber. States that higher atmospheric pressure outside pushes liquid up into the tube.
    • Source Reference: Section: “Air Pressure Applications”, Passage.
  • Q50 (Atmospheric Gravity & Density):
    • Required Points: Cites Earth’s gravitational force pulling air molecules closer to the planet’s surface. Explains that air density thins out as altitude increases.
    • Source Reference: Section: “Atmosphere”, Passage.
  • Q51 (Ozone Layer Protection):
    • Required Points: Identifies ozone layer location in the stratosphere. States its primary function is trapping and blocking harmful solar ultraviolet (UV) rays from reaching Earth.
    • Source Reference: Section: “Atmosphere & Layers”, Passage.
  • Q52 (Mesosphere Cosmic Shield):
    • Required Points: Mentions mesosphere altitude (up to 85 km). Explains that friction burns up incoming meteors and rock fragments, preventing surface impacts.
    • Source Reference: Section: “Layers of the Atmosphere”, Passage.
  • Q53 (Water Impurities):
    • Required Points: States that natural water accumulates foreign substances like leaves, mud, twigs, sand, and pathogenic germs. Defines these contaminants as impurities rendering water unsafe.
    • Source Reference: Section: “Water”, Passage.
  • Q54 (Soluble vs. Insoluble Impurities):
    • Required Points: Soluble impurities dissolve completely in water (Example: Salt). Insoluble impurities do not dissolve (Example: Sand or Twigs).
    • Source Reference: Section: “Soluble/Insoluble Impurities”, Passage.
  • Q55 (Sedimentation vs. Decantation):
    • Required Points: Sedimentation is the gravity settling of heavy insoluble particles at the bottom. Decantation is the pouring off of top clear water into another container without disturbing sediment.
    • Source Reference: Section: “Removal of Insoluble Impurities”, Passage.
  • Q56 (Filtration Limitation on Dissolved Solids):
    • Required Points: Explains that dissolved salt particles pass through microscopic paper pores along with water molecules. Defines filter paper as a physical sieve capable of stopping only undissolved suspended solids.
    • Source Reference: Section: “Filtration & Soluble Impurities”, Passage.
  • Q57 (Post-Purification Contamination):
    • Required Points: Identifies that purified municipal water travels through long underground pipeline networks. Mentions that leaks or dirty pipes can recontaminate water with germs before reaching household taps.
    • Source Reference: Section: “Journey of Water to Our Homes”, Passage.

Scenario-Based / Competency Rubric

  • Q58 (Mountaineering Air Density Scenario):
    • Key Rubric Points:
      1. Identifies that gravity pulls atmospheric air closest to sea level.
      2. States that moving up through atmospheric layers causes air to thin out.
      3. Explains that lower air density at high altitudes provides less oxygen per breath, causing breathing difficulty.
    • Source Reference: Passage.
  • Q59 (Salt Filtration Failure Scenario):
    • Key Rubric Points:
      1. Clarifies that filtration only separates insoluble suspended solids (sand) from liquid.
      2. Explains that dissolved salt forms a homogeneous liquid solution that passes completely through filter paper.
      3. Specifies that Rohan must perform thermal boiling/evaporation or distillation to separate dissolved salt from water.
    • Source Reference: Passage.
  • Q60 (Cardboard Tumbler Demonstration Scenario):
    • Key Rubric Points:
      1. Denies the presence of adhesives or glue.
      2. Explains that air molecules are in continuous motion in all directions, exerting force on surfaces.
      3. States that air pressure pushing upward against the cardboard from below is greater than the downward weight of water inside the glass, keeping the cardboard sealed.
    • Source Reference: Passage.
  • Q61 (Chlorine Shortage & Domestic Precautions Scenario):
    • Key Rubric Points:
      1. Identifies that lack of chlorination leaves harmful bacteria and disease-causing germs alive in tap water, risking waterborne illnesses.
      2. Recommends boiling water at home to thermally destroy pathogens.
      3. Recommends using domestic water filters to eliminate residual contamination.
    • Source Reference: Passage.
  • Q62 (Priya’s Water Conservation Strategy):
    • Key Rubric Points (Must list 5 valid rules from “Be Water Smart”):
      1. Turn off taps while brushing teeth or washing dishes.
      2. Place unused ice cubes on house plant soil instead of throwing them in the sink.
      3. Reuse water left over from washing fruits/vegetables to water house plants.
      4. Wash fruits/vegetables in a bowl of water rather than running water.
      5. Check and mend leaking pipeline fixtures promptly.
    • Source Reference: Passage.

Long-Answer / Essay Rubric

  • Q63 (Distillation Engine & Industrial Utility):
    • Key Rubric Points:
      1. Operational Mechanism: Describe heating salt solution in a round-bottom distillation flask over a burner.
      2. Vaporization & Separation: Liquid water boils into steam, leaving non-volatile dissolved impurities at the bottom of the flask.
      3. Condensation Unit: Steam passes into a water-cooled condenser tube, where cooling causes gas to condense back into liquid water.
      4. Collection: Pure water drips out into a receiving flask/beaker as distilled water.
      5. Industrial Applications (3 Required): Used in automobile batteries, scientific laboratories, and pharmaceutical industries.
    • Source Reference: Passage.
  • Q64 (Atmospheric Layers Comparative Matrix):
    • Key Rubric Points (Must cover all 5 layers with altitude & characteristics):
      1. Troposphere: 0–15 km; clouds, weather changes, breathable air.
      2. Stratosphere: 15–50 km; aircraft cruising path, protective ozone layer.
      3. Mesosphere: 50–85 km; burning of meteors and space debris.
      4. Thermosphere: 85–600 km; extreme temperatures (500°C–2000°C+), artificial satellites.
      5. Exosphere: 600–10,000 km; thinnest outer boundary, transition into deep space, satellites.
    • Source Reference: Passage.
  • Q65 (Municipal Water Supply Flowchart & Mechanics):
    • Key Rubric Points:
      1. Source Extraction: Pumping raw river/reservoir water into the treatment plant.
      2. Sedimentation Tank: Addition of coagulating chemicals to settle insoluble dirt into sludge.
      3. Filtration Bed: Draining water through structured layers of coal/charcoal, sand, and gravel to remove large and fine suspended impurities.
      4. Chlorination & Disinfection: Treating filtered water with chlorine in tanks to kill pathogenic bacteria causing waterborne diseases.
      5. Storage & Domestic Distribution: Pumping clean water into service reservoirs (overhead tanks) for municipal distribution.
    • Source Reference: Passage.
  • Q66 (Comprehensive Water Purification Framework):
    • Key Rubric Points:
      1. Insoluble Impurities:
        • Sedimentation: Gravity settling of heavy solids (sand/mud) in undisturbed liquid.
        • Decantation: Pouring clear top liquid off along a glass rod without disturbing sediment.
        • Filtration: Passing turbid liquid through a paper cone filter inside a funnel; residue stays on paper while filtrate passes through.
      2. Soluble Impurities:
        • Boiling / Evaporation: Heating solution to vaporize liquid water, leaving dissolved solid salt behind.
        • Distillation: Evaporating water in a flask and condensing steam in a condenser to capture ultra-pure distilled liquid.
    • Source Reference: Passage.
  • Q67 (Air Pressure Mechanics, Experiments & Devices):
    • Key Rubric Points:
      1. Definition: Physical force exerted by continuously moving air molecules striking surfaces in all directions.
      2. Experiment 1 (Cardboard Glass): Inverted water-filled tumbler held by upward atmospheric pressure pushing against cardboard from below.
      3. Experiment 2 (Candle Combustion / Inflation): Inflating balloons until internal wall pressure exceeds elasticity, causing bursting.
      4. Daily Life Devices (3 Required):
        • Drinking Straw: Sucking air lowers internal pressure, higher external air pressure pushes liquid up.
        • Syringes / Droppers: Squeezing/pulling reduces chamber pressure, atmospheric pressure fills cylinder.
        • Vehicle Tyres: Compressed air inside tyres supports heavy loads of bicycles, cars, trucks, and airplanes.
    • Source Reference: Passage.

Leave a Comment