Which gas forms the largest share of dry air by volume?
- A.Oxygen
- B.Nitrogen
- C.Argon
- D.Carbon dioxide
Correct answer
Explanation
The correct answer is B, nitrogen, which makes up about 78 per cent of dry air by volume. It is comparatively inert, so it dilutes oxygen and slows combustion, and it enters living things mainly through the nitrogen cycle in which bacteria fix it in a usable form.
Option A, oxygen, is second with about 21 per cent; it is essential for respiration and combustion, but a candidate who answers from importance rather than from quantity gets the question wrong. Option C, argon, is the most abundant of the inert gases in air at a little under one per cent. Option D, carbon dioxide, is only about four hundredths of one per cent, yet it matters out of all proportion to its quantity because it absorbs outgoing heat and drives the greenhouse effect, and its share is rising.
Read the full article: Atmosphere and Winds: Layers, Pressure Belts and Jet Streams
Practice Questions
View allThe ozone layer, which absorbs ultraviolet radiation, lies in which layer of the atmosphere?
- A.Troposphere
- B.Stratosphere
- C.Mesosphere
- D.Thermosphere
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Ozone is concentrated in the lower and middle stratosphere, and because it absorbs ultraviolet radiation the temperature of this layer rises with height instead of falling.
Read the full explanation →The normal lapse rate of temperature in the troposphere is about
- A.6.5 degrees Celsius per kilometre
- B.1 degree Celsius per kilometre
- C.10 degrees Celsius per kilometre
- D.0.65 degrees Celsius per kilometre
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This is the average rate at which air temperature falls as one rises through the troposphere, and it explains why hill stations are cooler than the plains and why high peaks carry snow even in the tropics.
Read the full explanation →Meteors entering the earth's atmosphere burn up mainly in which layer?
- A.Stratosphere
- B.Mesosphere
- C.Thermosphere
- D.Exosphere
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Although the air there is thin, it is dense enough to heat a body moving at cosmic speed by friction, so most meteors glow and are destroyed in this layer and are seen from the ground as shooting stars.
Read the full explanation →The warm and dry local wind known as the snow eater blows over which region?
- A.The eastern slopes of the Rockies in North America
- B.The northern slopes of the Alps in Europe
- C.The eastern slopes of the Andes in Argentina
- D.The northern edge of the Sahara
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The wind is the Chinook. It descends the leeward slope, is compressed and warmed as it sinks, and can raise the temperature sharply in a few hours; it melts or evaporates the snow cover, which is why herders call it the snow eater and why it is valued for exposing…
Read the full explanation →The hot and dry wind that blows over the northern plains of India in May and June is called
- A.Loo
- B.Foehn
- C.Mistral
- D.Bora
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It is a strong, hot and dry wind that blows during the day over the plains of north India and Pakistan in the peak of summer, raising temperatures sharply and causing heat stroke, and it dies down after sunset.
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