Chemistry 9th Chap 11 : Topic 1 - Maryam Publications

Chemistry Chapter 11 : Topic 1

Composition of Air

1 / 24

Which statement best describes the composition of clean, dry air?

A) It is a mixture of gases with varying proportions.

B) It is a pure substance with constant composition.

C) It contains only oxygen and carbon dioxide.

D) It is a compound of nitrogen and oxygen in fixed ratio.

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The approximate percentage of nitrogen in clean, dry air is:

A) 1%

B) 78%

C) 0.04%

D) 21%

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Oxygen gas in atmospheric air is approximately:

A) 1%

B) 78%

C) 0%

D) 21%

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The remaining 1% of air mainly consists of:

A) Water vapors only

B) Noble gases and carbon dioxide

C) Only hydrogen and helium

D) Only nitrogen compounds

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Which of the following gases is present in the smallest proportion in clean dry air?

A) Oxygen

B) Carbon dioxide

C) Argon

D) Nitrogen

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Air is considered homogeneous because:

A) Its composition is uniform throughout

B) It contains visible particles of gases

C) It can be separated by filtration

D) It contains only one type of gas

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Which gas is present in maximum amount in dry air?

A) Argon

B) Nitrogen

C) Oxygen

D) Carbon dioxide

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Which statement about carbon dioxide in air is correct?

A) It is the second most abundant gas.

B) It is absent in clean air.

C) It exists only in trace amount.

D) It is present in fixed 21% proportion.

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Noble gases in air include mainly:

A) Hydrogen and methane

B) Oxygen and nitrogen

C) Carbon dioxide and sulfur dioxide

D) Argon, helium, neon

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If oxygen in air is reduced significantly, the most immediate effect would be:

A) No biological effect

B) Increase in nitrogen production

C) Increase in CO₂ formation

D) Difficulty in respiration

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Air is classified as a mixture because:

A) It reacts chemically to form compounds.

B) It has fixed chemical formula.

C) It contains only one element.

D) It can be separated by physical means.

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Which of the following best represents correct order of gases in composition?

A) O₂>N₂>CO₂

B) O₂>CO₂>N₂

C) N₂>O₂ > other gases

D) CO₂>O₂>N₂

13 / 24

Which gas in air is chemically most unreactive?

A) Argon

B) Nitrogen

C) Oxygen

D) Carbon dioxide

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Clean dry air does NOT contain:

A) Water vapour

B) Argon

C) Nitrogen

D) Oxygen

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The percentage of oxygen in air is important because:

A) It supports combustion and respiration.

B) It is the main inert gas.

C) It makes air heavier than nitrogen.

D) It prevents rusting completely.

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Which gas is most responsible for maintaining atmospheric pressure balance?

A) Nitrogen

B) Ozone

C) Oxygen

D) Carbon dioxide

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If carbon dioxide percentage increases significantly in air, it may lead to:

A) Formation of oxygen gas

B) Global warming due to greenhouse effect

C) Increase in nitrogen fixation

D) Decrease in respiration rate of plants only

18 / 24

Which of the following correctly identifies air as a mixture?

A) Fixed ratio of gases always

B) Chemically bonded elements

C) Variable composition of gases

D) Single element substance

19 / 24

The gas used by plants in photosynthesis is:

A) Oxygen

B) Carbon dioxide

C) Argon

D) Nitrogen

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Why is nitrogen considered important in air despite being largely inert?

A) It burns easily.

B) It is toxic gas.

C) It supports combustion.

D) It is used in protein formation indirectly via nitrogen cycle.

21 / 24

A student claims air is a compound because it has fixed percentages of gases. This statement is:

A) Incorrect because air is not chemically combined.

B) Incorrect because air contains only oxygen.

C) Correct because nitrogen and oxygen form compounds.

D) Correct because all mixtures have fixed ratios.

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Which statement about noble gases in air is correct?

A) They form most of the air composition.

B) They are responsible for combustion.

C) They are present in trace amounts.

D) They are highly reactive.

23 / 24

The correct approximation of carbon dioxide in air is:

A) 0.04%

B) 0.4%

C) 40%

D) 4%

24 / 24

Which property confirms that air is a physical mixture?

A) It reacts explosively always.

B) It can be separated into components physically.

C) It has chemical formula.

D) It has fixed boiling point.

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