Assertion : Sb (III) is not precipitated as sulphide when in its alkaline solution `H_(2)S` is passed.
Reason : The concentration of `S^(2-)` ion in alkaline medium is inadequate for precipitation.

Options

A. If both assertion and reason are true and reason is the correct explanation of the assertion
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If the assertion and reason both are false.

Answer

To analyze the assertion and reason provided in the question, we can break it down step by step.

### Step 1: Understanding the Assertion
The assertion states that Sb(III) (antimony in the +3 oxidation state) is not precipitated as a sulfide when hydrogen sulfide (H₂S) is passed into its alkaline solution.

### Step 2: Understanding the Reason
The reason given is that the concentration of sulfide ions (S²⁻) in an alkaline medium is inadequate for precipitation.

### Step 3: Analyzing the Chemistry
1. **Antimony Chemistry**: Antimony (Sb) can exist in different oxidation states, with Sb(III) being one of them. In the presence of sulfide ions, Sb(III) can form antimony sulfide (Sb₂S₃), which is a precipitate.

2. **Role of Alkaline Medium**: In an alkaline solution, the concentration of sulfide ions (S²⁻) is indeed low because sulfide ions tend to react with hydroxide ions (OH⁻) to form polysulfides or other species.

3. **H₂S in Alkaline Medium**: When H₂S is introduced into an alkaline solution, it does not dissociate completely to provide sufficient S²⁻ ions. Instead, it remains largely in the form of HS⁻ or H₂S, which does not contribute to the precipitation of Sb₂S₃.

### Step 4: Conclusion
Based on the analysis, the assertion is true: Sb(III) does not precipitate as a sulfide in alkaline conditions when H₂S is passed. The reason is also true: the concentration of S²⁻ ions is inadequate for precipitation in an alkaline medium.

### Final Answer
Both the assertion and the reason are true, and the reason correctly explains the assertion.

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