EXERCISE 5.1 - IN READABLE - Q AND A FORMAT

Exercise 5.1: Air and Atmosphere (Q&A)

Section A: Fill in the Blanks

Question: Fill in the blank spaces by choosing the correct words in brackets.

• Question: Oxygen is necessary for respiration and ___________ [photosynthesis/combustion]

Answer: combustion

• Question: The envelope of air which surrounds the earth is known as ___________ [exosphere/atmosphere]

Answer: atmosphere

• Question: The life supporting constituent of air is ___________ [nitrogen/oxygen]

Answer: oxygen

• Question: When products of combustion are passed through anhydrous copper sulphate, it turns ___________ [yellow/blue]

Answer: blue


Question: When clear limewater is exposed to air for some time it turns ___________ [milky/pink]

Answer: milky


Section B: Correct the Statements

Statements given below are incorrect. Write the correct statements:

Question: The products of the combustion of a fuel are nitrogen and water vapour.

Correction:  The products of the combustion of a fuel are carbon dioxide and water vapour.


Question: Coal is a household fuel.

Correction: Coal is an industrial fuel.


Question: LPG is an incombustible gas kept in home to extinguish fire.

Correction: LPG is a combustible gas used as a household fuel.


Question: Water turns blue coloured anhydrous copper sulphate to colourless substance.

Correction: Water turns white anhydrous copper sulphate into a blue coloured substance.


Question: Oxygen is not necessary for the respiration of plants.

Correction: Oxygen is necessary for the respiration of plants.


Section C: Match the Following

Question: Match the statements:

Column I (Question)	Column II (Answer)
1. The products of combustion of a fuel.	(d) Water and carbon dioxide
2. Percentage of oxygen in air.	(e) 21%
3. Percentage of nitrogen present in air.	(a) 78%
4. A gas present in air which turns limewater milky.	(b) Carbon dioxide
5. A petroleum product commonly used as household fuel.	(c) Kerosene oil

Section D: True or False

Write ‘True’ or ‘False’:

Question: The ratio of oxygen and nitrogen by volume in air is about 1:4.

Answer: True


Question: Biomass is common household fuel in rural India.

Answer: True


Question: Raw materials for combustion are carbon dioxide and water.

Answer: False


Question: Coal is used as an industrial fuel.

Answer: True


Question: Nitrogen in the air helps in combustion.

Answer: False


Section E: Multiple Choice Questions

Tick (✓) the most appropriate answer.

Question: Atmosphere consists of:


Answer: (d) envelope of air around the earth


Question: The constituent of air which helps in combustion is:

Answer: (c) oxygen


Question: A gas which is commonly used as household fuel is:

Answer: (b) LPG


Question: The composition of air is:

Answer: (b) 21% oxygen, 78% nitrogen and 1% of other gases

Question: The products of the combustion of a fuel are:

Answer: (b) water vapour and carbon dioxide


Section F: Descriptive Answers

1. Question: Answer the following questions:

Question: Name four important constituents of air and state their appropriate percentage in composition.

Answer:

Nitrogen - (78.03%),

Oxygen - (20.9%),

Carbon dioxide - (0.03%).

Other gases - (0.94%) - Noble gases like Argon, Helium, Neon,Krypton, Xenon, Radon and Water Vapour and Ozone.


2. Answer the following

Question: (a) Name a major constituent of air which does not take part in the process of combustion.

 

Answer: Nitrogen

(b) Name a constituent of air which is essential for combustion and respiration. 

Answer: Oxygen 

(c) Name the constituent of air which is essential for photosynthesis.

Answer: Carbon dioxide.


3. Question: Briefly describe how you will prove the presence of following in air: 

(a) water vapour 

Answer: By placing ice in a glass tumbler; droplets appearing on the outside prove water vapour is present.

(b) carbon dioxide

Answer: By passing air through limewater; it turns milky, proving carbon dioxide is present.

4. Answer the Following

Question: (a) What do you understand by the term fuel? 

Answer: A material that burns to release a large amount of heat and light energy.

Question: (b) Name any four common household fuels. 

Answer: LPG, Kerosene, Wood, and Biogas.

Question: (c) Name the products formed during the combustion of a fuel.

Answer: Carbon dioxide, water vapour, and heat energy.

5. Question: How will you prove that air is necessary for the combustion of fuel?

Answer: By inverting a glass tumbler over a burning candle fixed in a trough of water; the candle goes out once the oxygen inside is consumed.

6. Question: How will you prove experimentally that products of the combustion of a candle are: 

(a) carbon dioxide gas (b) water vapour?

Answer: Use a suction pump to draw combustion gases through white anhydrous copper sulphate (which turns blue, proving water vapour) and then through limewater (which turns milky, proving CO2).

7. Question: State the main uses of the following gases: 

(a) nitrogen 

Answer: Nitrogen is used to preserve food and is vital for plant growth (nitrates).

(b) oxygen

Answer: Oxygen is used for respiration by living things and for the combustion of fuels.