Q1. [1] straightforward exam-ready
The green coating that forms on copper objects exposed to moist air is an example of:
(A) Rancidity
(B) Reduction
(C) Corrosion
(D) Precipitation
- A Rancidity
- B Reduction
- C Corrosion
- D Precipitation
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
(C) Corrosion
The green coating on copper is basic copper carbonate, formed when copper reacts with moist CO₂ in air. This is an example of corrosion.
Source: Chapter 1, Section 1.3.1; Chapter 3, Section 3.5
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Explanation
- Corrosion is the attack on a metal by substances like moisture or acids in its surroundings. The green coat on copper and black coat on silver are classic CBSE examples of corrosion.
- Rancidity refers to spoilage of fats/oils — eliminate it immediately.
- Reduction is loss of oxygen — the opposite of what happens here.
- Precipitation is formation of an insoluble salt in solution — not applicable here.
- Remember: rusting of iron, blackening of silver, and greening of copper are all examples of corrosion.