(i) `underset(("A morphous solid"))(A)underset(air)overset(O_(2))(to)Boverset("lime water")(to)"milky"`
(ii) Metal sulphide `overset("roasting")(to)underset(gas)Boverset(KMnO_(4)//H^(+))(to) "decolorisation of" KMnO_(4)`
(iii) `underset((gas))Boverset(Fe^(3+))toFe^(2+)`
Correct statement is

Options

A. A is FeO
B. B is `CO_(2)`
C. B is `SO_(2)`
D. A is ZnS

Answer

To solve the given question, we need to analyze each part of the statements provided and determine the correct chemical transformations and their implications.

### Step-by-Step Solution:

**(i)** The first part of the question describes a transformation of an "amorphous solid" A into B in the presence of air and oxygen (O₂), resulting in a "milky" solution when treated with lime water.

1. **Identify A**: The "amorphous solid" could refer to a non-crystalline form of a compound, such as silica (SiO₂) or a metal oxide.
2. **Transformation**: When this solid is heated in the presence of air and oxygen, it likely undergoes oxidation.
3. **Resulting B**: The product B could be a soluble compound, such as a metal oxide that reacts with water to form a solution.
4. **Lime Water Reaction**: Lime water (calcium hydroxide, Ca(OH)₂) turns milky when carbon dioxide (CO₂) is bubbled through it, forming calcium carbonate (CaCO₃). This suggests that the product B may be producing CO₂ when reacted with lime water.

**Conclusion for (i)**: The statement likely describes the oxidation of a metal or non-metal to form an oxide that reacts with water to produce CO₂, which then reacts with lime water to form a milky solution.

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**(ii)** The second part mentions a metal sulphide undergoing roasting to produce gas B, which is then treated with KMnO₄ in an acidic medium (H⁺) leading to the "decolorisation of KMnO₄".

1. **Identify Metal Sulphide**: Common metal sulphides include zinc sulphide (ZnS), lead sulphide (PbS), etc.
2. **Roasting Process**: Roasting typically involves heating the metal sulphide in the presence of oxygen, producing metal oxides and sulfur dioxide (SO₂) gas.
3. **Gas B**: The gas produced (SO₂) can reduce KMnO₄ in acidic conditions, leading to the decolorisation of the purple solution of KMnO₄.

**Conclusion for (ii)**: The statement describes the roasting of a metal sulphide to produce SO₂, which reduces KMnO₄, resulting in decolorisation.

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**(iii)** The third part indicates a transformation involving a gas and Fe³⁺ ions being reduced to Fe²⁺ ions.

1. **Identify the Reaction**: The gas mentioned could be a reducing agent, such as hydrogen (H₂) or carbon monoxide (CO).
2. **Reduction Process**: The Fe³⁺ ions are being reduced to Fe²⁺ ions, which is a common reduction reaction in redox chemistry.

**Conclusion for (iii)**: The statement describes a reduction process where a gas reduces Fe³⁺ to Fe²⁺.

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### Final Conclusion:
Based on the analysis of each part, the correct statements are as follows:
- (i) Describes the oxidation of a solid to produce a gas that reacts with lime water.
- (ii) Describes the roasting of a metal sulphide producing SO₂, which decolorises KMnO₄.
- (iii) Describes the reduction of Fe³⁺ to Fe²⁺ by a gas.