Question

Animals breathe in air rich in ________ and breathe out air rich in__________.

• A. oxygen, carbon dioxide
• B. carbon dioxide, oxygen
• C. oxygen, nitrogen
• D. nitrogen, carbon dioxide

Answer 1

The correct option is A

oxygen, carbon dioxide

Animals breathe in air rich in oxygen and breathe out air rich in carbon dioxide. The air that we inhale contains 78% nitrogen, 21% oxygen and small amounts of carbon dioxide, argon, neon, helium and hydrogen. The air that we exhale contains 4% to 5% by volume of carbon dioxide, about a 100 fold increase over the inhaled amount. The volume of oxygen is reduced by a small amount, 4% to 5%, compared to the oxygen inhaled.