An amorphous solid ‘A’ burns in air to form a gas ‘B’ which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aq. `KMnO_(4)` solution. Identify the solid ‘A’ and the gas ‘B’ and write the reaction involved.

Explanation

To solve the problem step by step, we need to identify the amorphous solid 'A' and the gas 'B' based on the clues provided.

### Step 1: Identify the gas 'B'
The question states that gas 'B' turns lime water milky. Lime water is a solution of calcium hydroxide, and it turns milky when carbon dioxide (CO₂) or sulfur dioxide (SO₂) is bubbled through it. Both gases can cause this reaction:

- **CO₂ + Ca(OH)₂ → CaCO₃ (s) + H₂O** (Lime water turns milky due to the formation of calcium carbonate)
- **SO₂ + Ca(OH)₂ → CaSO₃ (s) + H₂O** (Lime water can also turn milky due to the formation of calcium sulfite)

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