Science — AI-generated practice question

(a) This phenomenon is called acid rain. When the pH of rain water falls below 5.6, it is termed acid rain. It is caused by the dissolving of pollutant gases (like SO₂ and NO₂ released from industries) in rainwater, forming sulphuric and nitric acids, which lower the pH.

(b) When acid rain flows into rivers, it lowers the pH of river water. Living organisms can survive only within a narrow pH range. The reduced pH makes survival of aquatic life in such rivers difficult, as their metabolic processes are disrupted.

(c) Our body functions within a pH range of 7.0 to 7.8. All living organisms are highly pH-sensitive and can tolerate only a narrow range of pH change. A significant drop in environmental pH — as caused by acid rain — threatens biological processes essential for survival.

(d) Adding lime (calcium hydroxide / slaked lime) to the river water can neutralise the excess acid, raising the pH back to a range suitable for aquatic life.

Source: Chapter 2, Section 2.3.1 — Importance of pH in Everyday Life

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• The question has four sub-parts worth a combined 5 marks (~1–1.5 marks each), so keep each part to 2–3 lines.
• Examiners expect the term "acid rain" explicitly in (a) with a cause.
• For (b) and (c), directly quote/paraphrase the textbook line: "Living organisms can survive only in a narrow range of pH change" and "survival of aquatic life becomes difficult" — these are scoring phrases.
• For (d), any base that neutralises acid is acceptable; lime/slaked lime is the standard textbook-friendly answer. Don't over-explain the chemistry here.