15. AIR AROUND US 

---

Chapter-reviews: 

• The air contains nitrogen 79%, oxygen 21%, carbon dioxide 1%, some other gass, water vapour. Air also contains dust particles and smoke.  
• Oxygen is the gas, which is  essential for respiration.
• Air support burning.
• Moving air is called wind.
• Air occupies space. 
• The presence of water vapour in air is important for the water cycle in nature.
• The air contains water vapour.
• The envelope of air that surrounds the earth is known as atmosphere.
• Atmosphere is essential for life on earth.
• Aquatic animals use dissolved air in water for respiration.
• Plants and animals depend on each other for exchange of oxygen and carbon dioxide from air.
• Nitrogen gas is present in atmosphere in large amount. 
• Animals and plants both use oxygen for respiration and gaseous exchanges take place among themselves. 
• Animals cannot live without plants. Similarly, plants can not survive for long without animals.
• Windmills are also used to generate electricity. which run by the help of air. 
• Air also helps in the dispersal of seeds and pollen of flowers of several plants.
• Air plays an important role in water cycle.
   

15. AIR AROUND US 

---

Exercise: 

Q1: What is the composition of air?

Ans: The air contains nitrogen 79%, oxygen 21%, carbon dioxide 1%, some other gass, water vapour. Air also contains dust particles and smoke.  

Q2: Which gas in the atmosphere is essential for respiration?

Ans: Oxygen is the gas, which is  essential for respiration.

Q3: How will you prove that air supports burning?

Ans: When we light a  candle in a tub with some filled water and also cover the candle with inverted glass. We observe that the candle blows out after burning for some time, and the water level inside the inverted glass rises up to some
extent. The air component, oxygen is used in burning, so remains space is occupied by water and it rises up. This shows that air support burning. 

Q4: How will you show that air is dissolved in water?

Ans: When water is boiled in a pan, we notice that some  bubbles form around the inner surface of the pan. It means air is dissolving in water. 

Q5: Why does a lump of cotton wool shrink in water?

Ans: A lump of cotton wool shrinks when immersed in water. This is because air present in the cotton wool escapes. Thus, the volume of the cotton wool decreases.

Q6: The layer of air around the earth is known as ___________.

Ans: The layer of air around the earth is known as atmosphere.

Q7: The component of air used by green plants to make their food, is ______.

Ans: The component of air used by green plants to make their food, is carbon dioxide.

Q8: List five activities that are possible due to the presence of air.

Ans: 

(i) Respiration

(ii) Burning

(iii) Photosynthesis

(vi) Flying of kites

(v) Movement of sailing yachts, gliders, parachutes, airplanes

(vi) Generation of electricity by windmills

Q9: How do plants and animals help each other in the exchange of gases in the atmosphere?

Ans: All animals do respiration and they release carbon dioxide in the atmosphere and take oxygen during this process whereas, plants utilise carbon dioxide in the process of photosynthesis and release oxygen. Here we see that gaseous exchanges take place among animals and plants. 

15. AIR AROUND US 

---

Important Questions with solution: 

Question1: What is air ? 

Answer: Air is a mixture of various gases like nitrogen, oxygen, carbon dioxide and some other gases and smoke and dust particles. 

Question2: What is atmosphere? 

Answer: Our earth is surrounded by a thin layer of air. This layer extends up to
many kilometres above the surface of the earth and is called atmosphere.

Question3: Whch gas is carried by mountaineers while climbing up? 

Answer: Mountaineers carry oxygen gas in cylinders while climbing up.  

Question4: What is wind? 

Answer: Moving air is called wind. 

Question5: Why does Firki rotate?

Answer: When the fast-moving air exerts pressure on Firki, it rorates very fast. 

Question6: What is reason that when the air comes in the contact of cold surfaces, the drops of water become visible on the surfaces?  

Answer: When the air comes in the contact of cold surface, the water vapour present in air condensed and become water drops.

Question7: Which gas support burning? 

Answer: Oxygen. 

Question8: Which gas does not support burning? 

Answer: Nitrogen. 

Question9: In the presence of which gas do we feel suffocated? 

Answer: Carbon dioxide. 

Question10: Which gas is released on burning an object? 

Answer: Carbon dioxide. 

Question11: Which gas is used by plants and animals during respiration? 

Answer: Oxygen.

Question12: Which gas is released by plants and animals during respiration? 

Answer: Carbon dioxide. 

Question13: Which gas is used by green plants during the process of photosynthesis? 

Answer: Carbon dioxide. 

Question14: Which gas is released by green during food making process as product? 

Answer: Oxygen. 

Question15: Which gas is present in atmosphere in large amount? 

Answer: Nitrogen 79%. 

Question16: Why are long fireplaces (Chimaneys) installed in factories? 

Answer: Smokes have some gases and very tiny dust particles which are usually harmful. This is the reason to install long fireplaces (Chimaneys) in factory as they take the harmful smoke and gases away from our noses.

Question17: What are the role of fine hair and mucus present inside our nose?

Answer: When we inhale air during breathing through our nostrils. Fine hair and mucus are present inside the nose to prevent dust particles from getting into the respiratory system. 

Question18: How animals and plants are interdependence on each other? 

Answer: Animals and plants are interdependence on each other, because these organisms live on gaseous exchanges like oxygen and carbon dioxide. They would consume all the carbon dioxide in the atmosphere. We can see that both need each other, as the balance of oxygen and carbon dioxide in the atmosphere is thus maintained. This shows the interdependence of plants and animals. 

Question19: Write the some properties of air?  

Answer: 

Properties of air:

(i) Air occupies space. 

(ii) Air has no colour and one can see through it.

(iii) It is transparent. 

(iv) It fills the space. 

(v) Air apply force and has power to do work. 

Question20. What is windmill? 

Answer: The windmill is used to draw water from tubewells and to run flour
mills. Windmills are also used to generate electricity.

15. AIR AROUND US 

---

Exempler Problems: 

Multiple Choice Question: 

1. Which of the following statements is incorrect?

(a) All living things require air to breathe.
(b) We can feel air but we cannot see it.
(c) Moving air makes it possible to fly a kite.
(d) Air is present everywhere but not in soil.

2. Wind does not help in the movement of which of the following?

(a) Firki
(b) Weather cock
(c) Ceiling fan
(d) Sailing yacht

3. What is not true about air?

(a) It makes the windmill rotate.
(b) It helps in the movements of aeroplanes.
(c) Birds can fly due to presence of air.
(d) It has no role in water cycle.

4. Mountaineers carry oxygen cylinders with them because

(a) there is no oxygen on high mountains.
(b) there is deficiency of oxygen on mountains at high altitude.
(c) oxygen is used for cooking.
(d) oxygen keeps them warm at low temperature.

5. Boojho took an empty plastic bottle, turned it upside down and dipped its open mouth into a bucket filled with water. He then tilted the bottle slightly and made the following observations.

(i) Bubbles of air came out from the bottle.
(ii) Some water entered the bottle.
(iii) Nitrogen gas came out in the form of bubbles and oxygen got dissolved in water.
(iv) No bubbles formed, only water entered the bottle.

Which observations is/are correct?

(a) (i) and (ii)                  (b) (iv) only
(c) (iii) and (iv)                (d) (i) only

6. Which of the following components of air is present in the largest amount in the atmosphere?

(a) Nitrogen                          (b) Oxygen
(c) Water vapour                  (d) Carbon dioxide

7. The components of air which are harmful to living beings are:

(a) nitrogen and carbon dioxide.
(b) dust and water vapour.
(c) dust and smoke.
(d) smoke and water vapour.

8. Usha took a lump of dry soil in a glass and added water to it till it was completely immersed. She observed bubbles coming out. The bubbles contain

(a) water vapour                   (b) only oxygen gas
(c) air                                    (d) none of these

9. State whether the following statements are true or false. If false, correct them.

(a) Plants consume oxygen for respiration.
(b) Plants produce oxygen during the process of making their own food.
(c) Air helps in the movements of sailing yachts and glider but plays no role in the flight of birds and aeroplanes.
(d) Air does not occupy any space.

10. In a number of musical instruments, air plays an important role. Can you name some such instruments?

11. In the boxes of Column I the letters of some words got jumbled. Arrange them in proper form in the boxes given in Column II

12. Make sentences using the given set of words.

(a) 99%, oxygen, nitrogen, air, together
(b) Respiration, dissolved, animals, air, aquatic
(c) Air, wind, motion, called

13. A list of words is given in a box. Use appropriate words to fill up the blanks in the following statements:

Air, oxygen, wind, water vapour, mixture, combination, direction, road, bottles, cylinders.
(a) The ______ makes the windmill rotate.
(b) Air is a ______ of some gases.
(c) A weather cock shows the ______ in which the air is moving at that place.
(d) Mountaineers carry oxygen ______ with them, while climbing high mountains.

17. Explain the following observations very briefly

(a) A firki does not rotate in a closed area.
(b) The arrow of weather cock points towards a particular direction at a particular moment.
(c) An empty glass in fact is not empty.
(d) Breathing through mouth may harm you.

18. Write just a few sentences for an imaginary situation if any of the following gases disappear from the atmosphere:

(a) oxygen
(b) nitrogen
(c) carbon dioxide