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Find the compound 'A' from the following reaction sequences. A —aqua regia→ B —(1) KNO2/NH4OH (2) AcOH→ yellow ppt

1. ZnS
2. CoS
3. MnS
4. NiS

Correct answer: CoS

Solution

The reaction sequence indicates that compound 'A' undergoes a transformation in aqua regia, which typically dissolves metals, and then reacts with KNO2/NH4OH and AcOH to produce a yellow precipitate. Cobalt sulfide (CoS) is known to form a yellow precipitate under these conditions, confirming it as the correct option.

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