Air We Breathe — Practice

Question 1

Which gas makes up most of the air, and how much of it is there?

Accepted Answer

Nitrogen, at about 78 per cent.

Question 2

Which gas in air supports burning?

Accepted Answer

Oxygen, which makes up about 21 per cent of air.

Question 3

Which gas of the air do plants use to make their food?

Accepted Answer

Carbon dioxide, which is about 0.04 per cent of air.

Question 4

Name four causes of air pollution.

Accepted Answer

Vehicle exhaust, factory smoke, burning garbage or crop stubble, and bursting firecrackers.

Question 5

How would you show that air occupies space?

Accepted Answer

Push an empty upturned glass straight down into a bucket of water. The water does not fill the glass because the trapped air is already occupying that space.

Question 6

A lit candle is covered with a glass and soon goes out. Explain why.

Accepted Answer

Burning needs oxygen. Once the oxygen trapped under the glass has been used up, the flame cannot continue and dies.

Question 7

What are PM2.5 particles and why are they dangerous?

Accepted Answer

They are extremely tiny particles of dust and soot. Because they are so small they travel deep into the lungs and can even pass into the bloodstream.

Question 8

What does AQI stand for and what does a high reading mean?

Accepted Answer

Air Quality Index. A high reading means the air is badly polluted and unhealthy to breathe.

Question 9

Oxygen is the gas we need, yet only a fifth of air is oxygen. Why is it fortunate that the rest is mostly nitrogen?

Accepted Answer

Oxygen supports burning. Nitrogen is unreactive and dilutes the oxygen, so fires stay controllable. If air were mostly oxygen, any small flame would blaze out of control.

Question 10

Is air weightless? Support your answer.

Accepted Answer

No. Air has weight, roughly 1.2 kg for every cubic metre at sea level. An inflated balloon weighs slightly more than the same balloon deflated, which shows the air inside has mass.

Question 11

Suggest three things you personally can do to reduce air pollution, and explain how each helps.

Accepted Answer

Walk or cycle short distances, which avoids exhaust fumes altogether. Refuse firecrackers, which release smoke and fine particles. Plant and care for trees, which take in carbon dioxide and trap dust.

Practice — Air We Breathe

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