JEE Chemistry 2025 Question with Solution

Given: The reaction sequence is

Find: The compound $A$.

Aqua regia dissolves suitable metal sulfides or metals to give the corresponding metal ions in solution. The next step is identified from the observation of a yellow precipitate.

From the provided solution, the precipitate is taken to indicate a nickel compound. Therefore the species formed after treatment is associated with $\text{NiS}$.

Hence the starting compound $A$ is identified as $\text{NiS}$.

Therefore, the correct option is B.

Given: A compound $A$ on treatment with aqua regia gives $B$, and further treatment with $KNO_3$ and $NH_4OH$ gives a yellow precipitate.

Find: Which option matches $A$.

The solution states that the yellow precipitate suggests a nickel compound and concludes that the compound must be related to nickel.

Comparing the options:

• $CoS$
• $NiS$
• $ZnS$
• $MnS$

Only $NiS$ contains nickel.

So, matching the solution's conclusion, $A = \text{NiS}$.

Therefore, the correct option is B.