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Air and Atmosphere — Homi Bhabha Class 6 Chemistry MCQs with Solutions
Free Homi Bhabha Class 6 Chemistry Air and Atmosphere MCQs with step-by-step solutions covering Composition of Air, Importance of Gases, Atmospheric Pressure, Air Pollution & Prevention. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Composition of Air · easy · theory
Which gas is present in the largest amount in air?
A. Water vapour
B. Carbon dioxide
C. Oxygen
D. Nitrogen ✓ Correct
Solution: Nitrogen makes up about 78% of air, far more than any other gas.
Q2 — Composition of Air · easy · theory
About one-fifth (nearly 21%) of the air is made up of which gas?
A. Hydrogen
B. Oxygen ✓ Correct
C. Carbon dioxide
D. Nitrogen
Solution: Oxygen makes up about 21% of air, which is roughly one-fifth of it.
Q3 — Composition of Air · easy · theory
Air is best described as …
A. A type of liquid
B. A mixture of several gases ✓ Correct
C. A single pure gas
D. A kind of metal
Solution: Air is a mixture of many gases such as nitrogen, oxygen and carbon dioxide, not a single pure gas.
Q4 — Composition of Air · easy · theory
Roughly how much of the air is nitrogen?
A. About 21%
B. About 50%
C. About 3%
D. About 78% ✓ Correct
Solution: Nitrogen forms about 78% of air, making it the most common gas in the air.
Q5 — Importance of Gases · easy · theory
Which gas in the air do humans and animals need for breathing?
A. Nitrogen
B. Carbon dioxide
C. Oxygen ✓ Correct
D. Water vapour
Solution: Living things use oxygen from the air to breathe and stay alive.
Q6 — Importance of Gases · easy · theory
Which gas do green plants use from the air to make their food?
A. Carbon dioxide ✓ Correct
B. Oxygen
C. Nitrogen
D. Hydrogen
Solution: Green plants take in carbon dioxide from the air and use it, with sunlight, to make their food.
Q7 — Importance of Gases · easy · theory
Which gas helps things burn?
A. Oxygen ✓ Correct
B. Nitrogen
C. Water vapour
D. Carbon dioxide
Solution: Oxygen supports burning; a fire cannot keep burning without oxygen.
Q8 — Importance of Gases · easy · theory
Which gas is often used in fire extinguishers to put out fires?
A. Oxygen
B. Carbon dioxide ✓ Correct
C. Hydrogen
D. Nitrogen
Solution: Carbon dioxide does not support burning and cuts off the oxygen, so it is used to put out fires.
Q9 — Atmospheric Pressure · easy · theory
The push of air on everything around us is called …
A. Air (atmospheric) pressure ✓ Correct
B. Magnetic force
C. Water pressure
D. Sound
Solution: Air presses on everything it touches; this push is called air pressure or atmospheric pressure.
Q10 — Atmospheric Pressure · easy · theory
The thick blanket of air that surrounds the Earth is called the …
A. Ocean
B. Atmosphere ✓ Correct
C. Rainbow
D. Ground
Solution: The layer of air wrapped around the Earth is called the atmosphere.
Q11 — Atmospheric Pressure · easy · theory
Air pressure acts …
A. In all directions ✓ Correct
B. Only downwards
C. Only sideways
D. Only upwards
Solution: Air pushes in all directions — up, down and sideways — not just one way.
Q12 — Atmospheric Pressure · easy · theory
Does air have weight?
A. Only smoke has weight
B. No, air has no weight
C. Air weighs nothing at all
D. Yes, air has weight ✓ Correct
Solution: Air is made of gases that do have weight, which is why the atmosphere presses down on us.
Q13 — Air Pollution & Prevention · easy · theory
Air pollution means that the air has …
A. Only clean oxygen
B. More nitrogen than usual
C. Pure water in it
D. Harmful substances mixed into it ✓ Correct
Solution: Air pollution is when harmful gases, smoke or dust get mixed into the air, making it unhealthy.
Q14 — Air Pollution & Prevention · easy · theory
Which of these adds smoke and harmful gases to the air?
A. Green growing trees
B. Smoke from vehicles and factories ✓ Correct
C. A garden of flowers
D. A clean flowing river
Solution: Vehicles and factories burn fuel and release smoke and harmful gases that pollute the air.
Q15 — Air Pollution & Prevention · easy · theory
Which of these helps keep the air clean?
A. Burning garbage
B. Planting more trees ✓ Correct
C. Running factories without filters
D. Driving more cars
Solution: Trees take in carbon dioxide and give out oxygen, so planting more trees helps keep the air clean.
Q16 — Air Pollution & Prevention · easy · theory
Trees help clean the air because they …
A. Give out thick smoke
B. Make a lot of dust
C. Take in oxygen and give out smoke
D. Take in carbon dioxide and give out oxygen ✓ Correct
Solution: Trees take in carbon dioxide and release oxygen, which freshens the air we breathe.
Q17 — Composition of Air · hard · theory
Nitrogen and oxygen together make up about what part of the air?
A. About 3%
B. About 21%
C. About half
D. About 99% ✓ Correct
Solution: Nitrogen (about 78%) and oxygen (about 21%) together make up about 99% of air.
Q18 — Composition of Air · hard · theory
One reason we say air is a mixture and not a single pure gas is that …
A. It is made only in factories
B. It cannot be separated at all
C. It has just one gas in it
D. It can be separated into different gases like oxygen and nitrogen ✓ Correct
Solution: Air can be separated into its different gases, which shows it is a mixture of several gases and not one pure gas.
Q19 — Importance of Gases · hard · theory
Air does not burn up everything very quickly even though it contains oxygen. This is mainly because nitrogen …
A. Adds more oxygen to the fire
B. Burns even faster than oxygen
C. Cools the Sun
D. Does not support burning and slows it down ✓ Correct
Solution: Nitrogen does not support burning, so it dilutes the oxygen in air and keeps things from burning too fast.
Q20 — Importance of Gases · hard · theory
To test whether a gas is carbon dioxide, we pass it through lime water. If it is carbon dioxide, the lime water turns …
A. Deep blue
B. Milky (cloudy white) ✓ Correct
C. Grass green
D. Bright red
Solution: Carbon dioxide turns clear lime water milky (cloudy white), which is the common test for this gas.
Q21 — Atmospheric Pressure · hard · theory
Our ears sometimes feel blocked when a plane climbs high or we go up a tall mountain. This happens because …
A. There is no air at all up there
B. The engine is too loud
C. The air pressure outside drops and no longer matches the pressure inside our ears ✓ Correct
D. The air becomes colder
Solution: Higher up, the outside air pressure is lower, so it no longer matches the pressure inside our ears, making them feel blocked.
Q22 — Atmospheric Pressure · hard · theory
An empty plastic bottle is tightly capped at the top of a high mountain and then brought down to the plains. In the plains it gets slightly crushed inward because …
A. There is no air in the plains
B. The higher air pressure in the plains presses in on it ✓ Correct
C. The bottle became heavier
D. The plastic melted on the way down
Solution: The air sealed inside is at the low mountain pressure, but the plains have higher air pressure, which presses the bottle inward.
Q23 — Air Pollution & Prevention · hard · theory
In winter, big cities are often covered by a mix of smoke and fog that makes it hard to see and breathe. This is called …
A. Dew
B. Steam
C. A rainbow
D. Smog ✓ Correct
Solution: Smog is a mixture of smoke and fog; the word itself comes from "smoke" and "fog".
Q24 — Air Pollution & Prevention · hard · theory
Factories can reduce the smoke they release into the air by …
A. Burning more coal
B. Building taller houses nearby
C. Fitting filters in their chimneys to trap harmful particles ✓ Correct
D. Running day and night without stopping
Solution: Filters fitted in chimneys trap the harmful smoke particles before the gases are let out, reducing air pollution.
Q25 — Composition of Air · medium · theory
Which gas is present in air in only a very small amount, about 0.03%?
A. Argon
B. Oxygen
C. Carbon dioxide ✓ Correct
D. Nitrogen
Solution: Carbon dioxide is only about 0.03% of air, a very small amount compared with nitrogen and oxygen.
Q26 — Composition of Air · medium · theory
Which of these is NOT a normal part of clean air?
A. Smoke ✓ Correct
B. Nitrogen
C. Oxygen
D. Carbon dioxide
Solution: Clean air has nitrogen, oxygen and a little carbon dioxide; smoke is a pollutant and is not part of clean air.
Q27 — Composition of Air · medium · numerical
Air is about 21% oxygen. In 100 litres of air, about how many litres are oxygen?
A. 78 litres
B. 100 litres
C. 21 litres ✓ Correct
D. 1 litre
Solution: 21% of 100 litres = 21 litres, so about 21 litres of the air is oxygen.
Q28 — Composition of Air · medium · theory
The amount of which gas in air keeps changing from place to place and day to day?
A. Nitrogen
B. Water vapour ✓ Correct
C. Argon
D. Oxygen
Solution: The amount of water vapour in air is not fixed; it changes with the weather and the place.
Q29 — Importance of Gases · medium · theory
When we breathe out, which gas do we give out more of?
A. Carbon dioxide ✓ Correct
B. Nitrogen
C. Hydrogen
D. Oxygen
Solution: Our body uses up oxygen and gives out more carbon dioxide when we breathe out.
Q30 — Importance of Gases · medium · theory
Packets of chips are often filled with nitrogen gas because nitrogen …
A. Dissolves the oil in the chips
B. Makes the chips tasty
C. Is unreactive and keeps the food fresh ✓ Correct
D. Helps the chips burn
Solution: Nitrogen does not react easily, so it keeps the chips fresh and stops them from going stale.