Why can acid rain be harmful to aquatic organisms?

Correct answer: It can lower the pH of water

The governing concept is pH and the effect of acidity on living organisms. Acid rain introduces acidic substances into lakes, ponds and rivers, so the water’s pH may fall below its normal range. Many aquatic organisms, eggs and plants are sensitive to such changes, which can disturb biological processes. Therefore option A is correct; sweetness, permanent alkalinity and colour alone do not explain the harm.