Chapter 26: AIR AND WATER

Chapter 26: Air and Water Class 10 Science and Technology (212) NIOS Textbook Solutions

Chapter 26. AIR AND WATER

INTEXT QUESTIONS 26.1

1. A chemical substance may occur as an element, mixture or compound. To which category does air belong?

Answer: Air belongs to the mixture category because it contains different gases physically mixed together, not chemically combined.

2. Name the major constituents of air. Which constituents are inevitable for survival of plants and animals?

Answer: Major constituents of air are nitrogen and oxygen.
The constituent inevitable for survival of plants and animals is oxygen.

3. If you were to compare the relative amounts of nitrogen and oxygen in the atmosphere. Which will be four times the other?

Answer: Nitrogen is about four times the amount of oxygen in the atmosphere .

4. Air also contains water vapour. But is its percentage in air the same at all places?

Answer: No, the percentage of water vapour in air is not the same at all places. It varies from place to place depending on climate and weather conditions.

INTEXT QUESTIONS 26.2

1. Why is oxygen essential for life? What would happen if there is no oxygen in air?

Answer: Oxygen is essential for life because it is needed for respiration in plants and animals to release energy from food. If there is no oxygen in air, animals would die and life would not survive.

2. Carbon dioxide acts as food for plants. Name the process in which it is utilized for making food.

Answer: Carbon dioxide is used by plants to make food through the process of photosynthesis.

3. What is dry ice and what is it used for?

Answer: Dry ice is the solid form of carbon dioxide (CO₂). It is used as a refrigerant to keep things cold, especially during storage and transport of food and other materials.

4. If you were to analyse all proteins, you would find a particular element common to all. Which one is it?

Answer: The element common to all proteins is nitrogen.

INTEXT QUESTIONS 26.3

1. What happens to atmospheric pressure as we climb a mountain?

Answer: As we climb a mountain, atmospheric pressure decreases with altitude because the air becomes thinner at higher heights.

2. At high altitude the people find their nose bleeding. Why?

Answer: It is because the blood pressure in blood vessels of the body is much more than the air pressure at high altitude, so the capillaries burst and bleeding occurs.

3. Which layer of atmosphere is the closest to the earth’s surface and which is the farthest from earth’s surface?

Answer: (i) The layer closest to the Earth’s surface is the Troposphere.
(ii) The layer farthest from the Earth’s surface is the Thermosphere.

4. In which layer of atmosphere is ozone layer present?

Answer: The ozone layer is present in the Stratosphere.

5. Name (i) a green house gas (ii) gas responsible for acid rain (ii) chemicals causing ozone hole

Answer: (i) A greenhouse gas: Methane
(ii) Gas responsible for acid rain: Sulphur oxides (SOx)
(iii) Chemicals causing ozone hole: Chlorofluorocarbons (CFCs)

INTEXT QUESTIONS 26.4

1. It is said that more of earth is water than land. How much of the earth’s surface is covered by water?

Answer: About three-fourths (3/4) of the Earth’s surface is covered by water.

2. Name any two sources of water.

Answer: Two sources of water are rain and sea.

3. Is rainwater pure or impure? Give one reason to support your answer.

Answer: Rainwater is pure (distilled water) because it is formed by evaporation and condensation, which remove most impurities.

4. What does chlorination do to water in order to purify it?

Answer: Chlorination kills harmful microorganisms (germs and bacteria) present in water, making it safe for drinking.

5. I could not form lather with soap while washing my hands, which type of water was it?

Answer: I could not form lather with soap while washing my hands because the water was hard water.

6. Name the type of hardness caused to water due to presence of bicarbonates of .

Answer: The hardness caused due to the presence of bicarbonates of Ca²⁺ or Mg²⁺ in water is called temporary hardness.

7. Name the type of hardness caused to due to presence-of chloride or sulphate of.

Answer: The hardness caused due to the presence of chlorides or sulphates of Ca²⁺ or Mg²⁺ in water is called permanent hardness.

8. Which type of hardness is removed by the following:

(i) boiling _____________

(ii) ion exchange method. ______________

Answer: (i) Boiling temporary hardness
(ii) Ion exchange method permanent hardness

9. Is water a polar or a non polar solvent? Why do you think so?

Answer:  Water is a polar solvent because its molecules have unequal distribution of electric charge. Oxygen attracts electrons more strongly than hydrogen, creating a positive and a negative end. This polarity helps water dissolve many ionic and polar substances.

10. At what temperature does water take up least space?

Answer: Water takes up the least space at 4°C because at this temperature its density is maximum.

INTEXT QUESTIONS 26.5

1. State any two uses of harvesting rain water?

Answer: Two uses of harvesting rain water are:

(i) It conserves valuable ground water.

(ii) It reduces local flooding and drainage problems,

(iii) It decreases landscaping and property maintenance needs

(iv) It provides quality water for many household needs;

(v) It can be used for domestic purposes (Any two)

2. How would industries and agriculture suffer in the event of acute scarcity of water?

Answer: In the event of acute scarcity of water:

Industries: coolant purpose, production of steam, use as solvent for many chemical would be affected

Agriculture: irrigation of crops, germination of seeds and growth of plants would be affected.

3. What does rainwater do to ground water?

Answer: Rainwater raises the declined groundwater level by recharging underground water sources.

4. Why does rain water prove to be suitable for washing with soap?

Answer: Rain water is suitable for washing with soap because it is in the form of soft water and easily forms lather with soap.

TERMINAL EXERCISES

1. Multiple choice type questions.

i. Air is

(a) compound

(b) element

(c) mixture

(d) non of these

Answer: (c) mixture .

[ Air is a mixture because it contains different gases like nitrogen, oxygen, carbon dioxide and water vapour.]

ii. Major components of air are

a) CO₂ and H₂O

b) N₂ and O₂ 

c) CO₂ and He

d) H₂O and Xe

Answer: (b) N₂ and O₂ .

[ Air mainly contains nitrogen (N₂) and oxygen (O₂).]

iii. The instrument used to measure humidity is

(a) barometer

(b) hygrometer

(c) lactometer

(d) thermometer

Answer: b) hygrometer .

[ A hygrometer is used to measure the amount of moisture (humidity) present in the air.]

iv. Water has maximum density at

(a) 0°C       (b) 10 °C           (c) 5°C        (d) 4 °C

Answer: (d) 4°C .

[ Water has maximum density at 4°C.]

2. List the utility of oxygen and nitrogen in our lives.

Answer: Utility of Oxygen:

(i) Oxygen is necessary for respiration in almost all living beings.

(ii) It supports combustion, so materials burn easily in its presence.

(iii) Oxygen is given to patients suffering from asthma, gas poisoning and for artificial respiration in hospitals.

Utility of Nitrogen:

(i) Nitrogen subdues the activity of oxygen, preventing rapid combustion and oxidation.

(ii) Nitrogen compounds help plants manufacture proteins, which animals and humans obtain through food.

(iii) Protein deficiency in growing children can cause Kwashiorkor.

3. What is atmospheric pressure?

Answer:  The weight of air column acting per unit area results in a pressure exerted by atmosphere called the atmospheric pressure.

4. How does the atmospheric pressure depend on altitude?

Answer: Atmospheric pressure decreases with increase in altitude because the density of air becomes lower at higher places, so less air presses down.

5. Give an activity, which proves that air exerts pressure.

Answer: Take an empty bottle of mineral water. Put some hot water in it and tightly screw the cap to make it airtight. Then pour cold water on the bottle. The bottle gets compressed because atmospheric air exerts pressure from outside, proving that air exerts pressure.

6. What is relative humidity?

Answer: Relative humidity is the ratio of the mass of water vapour actually present in a certain volume of air at room temperature to the mass of water vapour required to saturate the same volume of air at that temperature.

7. What is the different source of water? Mention any two.

Answer: Two different sources of water are:

(i) Rain water: It is considered the purest natural form of water. It is formed when water evaporates and later condenses into clouds and falls as rain.

(ii) Sea water: It is the largest natural source of water but contains high salinity and impurities, so it is not suitable for drinking.

8. Why is water called as universal solvent?

Answer: Water is called a universal solvent because it can dissolve a large number of substances such as solids like common salt and sugar and gases like oxygen and carbon dioxide. Therefore, it is one of the best and most useful solvents.

9. What are the different ways to purify drinking water? What is the role of chlorination?

Answer: Different ways to purify drinking water are sedimentation, filtration, boiling, distillation and chlorination. These methods help to remove impurities and harmful substances from water.

Chlorination is the process of adding chlorine to water to kill harmful germs and microorganisms, making the water safe for drinking.

10. What do you mean by hard and soft water? Explain the types of hardness in water.

Answer: Soft water is the water that forms lather easily with soap and is suitable for washing.
Hard water is the water that does not form lather easily with soap because of dissolved salts.

There are two types of hardness in water:

(i) Temporary hardness: It is caused by dissolved bicarbonates of calcium and magnesium and can be removed by boiling.

(ii) Permanent hardness: It is caused by dissolved chlorides and sulphates of calcium and magnesium and cannot be removed by boiling.

11. How are the temporary and permanent hardness removed from water?

Answer: Temporary hardness of water is removed by boiling, because the dissolved bicarbonates of calcium and magnesium get separated. Permanent hardness is removed by adding washing soda or by using ion exchange methods, as boiling cannot remove it.

12. Explain the following properties of water.

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13. (i) Surface tension

(ii) Density

Answer: (i) Surface tension: Surface tension is the property of water due to which its surface behaves like a stretched elastic layer. It occurs because water molecules attract each other strongly. Due to surface tension, small insects can walk on water and water forms droplets.

(ii) Density: Density is the mass of water present in a unit volume. Water has a maximum density at 4°C. Ice is less dense than water, so it floats on the surface of water.

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14. What is rainwater harvesting? How is it beneficial for everyday life?

Answer: Rainwater harvesting is the process of collecting and storing rainwater for future use instead of letting it flow away. It is beneficial in everyday life because it helps to recharge groundwater, raises the declined water level and provides water for domestic use during times of shortage.

15. Why is the presence of carbon dioxide in atmosphere essential? Give two reasons.

Answer: The presence of carbon dioxide in the atmosphere is essential because:

(i) It is required by green plants for photosynthesis to prepare food.

(ii) It helps in maintaining the heat balance of the Earth by trapping heat in the atmosphere.

16. Give any two medical uses of oxygen.

Answer: Two medical uses of oxygen are:

(i) Oxygen is given to the patients suffering from asthma or gas poisoning and for artificial respiration in hospitals.

(ii) A mixture of oxygen and nitrous oxide is used as anesthesia in surgical operations.

17. What are primary and secondary air pollutants? Give one example of each.

Answer: Primary air pollutants: These are pollutants that are directly emitted into the atmosphere from various sources.
Example: Carbon monoxide (CO) released from the exhaust of motor vehicles.

Secondary air pollutants: These are pollutants that are not emitted directly into the atmosphere but are formed when primary pollutants react with each other in the air.
Example: Ozone (O₃).

18. What are the sources of the following pollutants : (i) Chlorofluorocarbons (ii) Nitrogen oxides (iii) Particulate matter

Answer: (i) Chlorofluorocarbons (CFCs): These are released from refrigerants used in air conditioners and refrigerators. They are harmful to the ozone layer.

(ii) Nitrogen oxides (NOx): These are mainly produced by burning of fuels in vehicles and industries. Nitrogen dioxide (NO₂) is a reddish-brown gas with a pungent smell and indirectly causes acid rain.

(iii) Particulate matter (SPM): These come from volcanoes, dust storms and burning of fuels. They consist of tiny solid or liquid particles suspended in air and can cause breathing, heart and lung diseases.

19. Why are the following substances considered air pollutants: (i) Carbon monoxide (ii) Carbon dioxide (iii) Sulphur oxides (iv) Volatile organic compounds.

Answer: (i) Carbon monoxide (CO): It is a poisonous gas that reduces the oxygen-carrying capacity of blood.

(ii) Carbon dioxide (CO₂): It is a greenhouse gas that causes global warming and climate change.

(iii) Sulphur oxides (SOₓ): They cause acid rain and irritate the respiratory system.

(iv) Volatile organic compounds (VOCs): They react with other pollutants to form photochemical smog and can cause health problems.

20. What are (i) photochemical smog and (ii) ground level ozone.

Answer: (i) Photochemical smog: It is a mixture of smoke and fog formed by the action of sunlight (UV rays) on pollutants in the air. It prevents the dispersion of pollutants and causes breathing problems.

(ii) Ground-level ozone: It is formed when nitrogen oxides (NOₓ) react with volatile organic compounds (VOCs) in the presence of sunlight. It is a component of smog and is harmful to humans and animals when inhaled.

21. What are (i) point source pollution and (ii) non-point source pollution? Give one example of each.

Answer: (i) Point source pollution: It is pollution that comes from a single, identifiable source.
Example: Wastewater discharged from a factory through a pipe.

(ii) Non-point source pollution: It is pollution that comes from many scattered sources and cannot be traced to one specific point.
Example: Fertilisers and pesticides washed from agricultural fields by rain.

22. Dive any two of water for each of the following purposes (i) domestic (ii) industrial and (iii) agricultural

Answer: (i) Domestic uses of water:

(a) Drinking and cooking for human consumption and food preparation.

(b) Washing and cleaning for bathing, laundry, and maintaining household sanitation.

(ii) Industrial uses of water:

(a) As a coolant in thermal power plants and factories to absorb heat.

(b) As a solvent or raw material in industries such as paper, textile, and chemical manufacturing.

(iii) Agricultural uses of water:

(a) Irrigation of crops through canals, wells, or sprinkler systems.

(b) Livestock rearing by providing drinking water to cattle and other farm animals.

23. What do you mean by conservation of water? How is it useful?

Answer: Conservation of water means the careful and wise use of water to prevent its wastage and ensure that enough water is available for present and future generations.

Usefulness of water conservation:

(a) It helps to reduce the wastage of water.

(b) It ensures the availability of water during dry seasons and droughts.

(c) It helps to maintain the groundwater level.

(d) It protects the environment and supports agriculture, industries, and domestic needs.

(e) It ensures a sustainable supply of water for future generations.

24. You are incharge of the residents welfare association./ prepare two slogans to make residents aware of need for conservation of water.

Answer: Two slogans to create awareness about water conservation:

(i) "Save Water Today, Secure Tomorrow!"

(ii) "Every Drop Counts – Conserve Water, Protect Life!"

25. The atmospheric envelop around living beings is the provider of the gases essential for their survival which are these gases, what is their proportion in air and how are they responsible for survival?

Answer: The atmosphere is a layer of gases surrounding the Earth. It provides the gases essential for the survival of living organisms.

Gas	Proportion in Air (%)	Role in Survival
Nitrogen	78.03	It helps plants make proteins after nitrogen fixation, which is essential for the growth of all living organisms.
Oxygen	20.09	It is essential for respiration, through which living organisms release energy from food.
Carbon dioxide	0.033	It is used by green plants during photosynthesis to prepare food and release oxygen.
Other gases (argon, neon, helium, etc.)	0.942	These gases are present in small amounts and help maintain the composition of the atmosphere.

26. How does rain water pollute water bodies with the air pollutants ?

Answer: Rainwater dissolves harmful gases and other pollutants present in the air, such as sulphur dioxide, nitrogen oxides, and dust particles. When it falls on the earth, it carries these pollutants into rivers, lakes, ponds, and other water bodies. This pollutes the water, makes it unsafe for drinking and aquatic life and may also lead to acid rain, which further harms plants, animals and the environment.

27. Recall five properties of water and write a paragraph justifying that water is an indispensible resource.

Answer: Five Properties of Water:

(i) Universal Solvent: Dissolves more substances than any other liquid.

(ii) Hard Water: Contains dissolved calcium and magnesium salts; does not lather easily with soap.

(iii) Soft Water: Contains no or very few dissolved salts; lathers easily with soap.

(iv) Conversion of Hard Water into Soft Water: Done by boiling, adding washing soda, or using ion-exchange resins.

(v) Polar Nature: Water molecules have a partial positive charge on hydrogen and partial negative charge on oxygen, making it a polar molecule.

(vi) Surface Tension: The cohesive force at the surface allows water to form droplets and support light objects.

(vii) Capillarity (Rise of Water): Water rises in narrow tubes due to adhesive and cohesive forces, essential for plant water transport.

(viii)Density of Water: Water is densest at 4°C (1 g/cm³); ice is less dense and floats, insulating aquatic life in winter.

Water is an indispensable resource because its unique properties make life possible. As a universal solvent, it dissolves and transports nutrients, minerals, and waste products in living organisms. Its polar nature enables it to dissolve many ionic and polar substances that are essential for life processes. Surface tension and capillary action help water move from the roots to the leaves of plants, supporting photosynthesis and plant growth. The unusual property of ice being less dense than liquid water allows it to float, protecting aquatic life during winter. Hard water contains useful minerals such as calcium and magnesium, while soft water is more suitable for washing and other domestic purposes. Hard water can also be softened to make it suitable for different uses. Thus, water is essential for living organisms, agriculture, industries and maintaining ecological balance. Without water, life on Earth would not be possible.   

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28. How does boiling of hard water convert it such that it can be used for washing clothes?

Answer: Boiling removes temporary hardness of water. When hard water is boiled, the dissolved bicarbonates of calcium and magnesium decompose to form insoluble carbonates, which settle at the bottom as a precipitate. After removing this precipitate, the water becomes soft. Soft water forms lather easily with soap, making it suitable for washing clothes.

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