The components of air which are harmful to living beings are
(a) nitrogen and carbon dioxide
(b) dust and water vapour
(c) dust and smoke
(d) smoke and water vapour

Correct Answer: (c) dust and smoke

Explanation:  Dust and smoke are the harmful components in air. Water vapour, nitrogen and carbon dioxide are useful to living beings. Water vapour is important for the water cycle in nature. Nitrogen is necessary for plants. Carbon dioxide is essential for photosynthesis.