Multiple choice

Oxygen is returned to the atmosphere through

  1. combustion

  2. respiration

  3. photosynthesis

  4. oxidation

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process, i.e. photosynthesis.