Assertion : Stannous chloride gives grey precipitate with mercuric chloride , but stannic chloride does not do so.
Reason : Stannous chloride is a powerful oxidising agent which oxidises mercuric chloride to metallic mercury .

Options

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

Explanation

### Step-by-Step Solution:

1. **Understanding the Compounds**:
- Stannous chloride (SnCl₂) contains tin in the +2 oxidation state (Sn²⁺).
- Stannic chloride (SnCl₄) contains tin in the +4 oxidation state (Sn⁴⁺).

2. **Analyzing the Assertion**:
- The assertion states that stannous chloride gives a gray precipitate with mercuric chloride (HgCl₂), while stannic chloride does not.
- When SnCl₂ reacts with HgCl₂, it forms a gray precipitate of mercury (Hg) and stannic chloride (SnCl₄).

3. **Chemical Reaction**:
- The reaction can be represented as:
\[ \text{SnCl}_2 + \text{HgCl}_2 \rightarrow \text{SnCl}_4 + \text{Hg} \]
- In this reaction, Sn²⁺ is oxidized to Sn⁴⁺, while Hg²⁺ is reduced to metallic mercury (Hg).

4. **Analyzing the Reason**:
- The reason states that stannous chloride is a powerful oxidizing agent that oxidizes mercuric chloride to metallic mercury.
- However, this is incorrect because stannous chloride acts as a reducing agent in this reaction, not an oxidizing agent.

5. **Conclusion**:
- The assertion is true because stannous chloride does produce a gray precipitate of mercury when reacting with mercuric chloride.
- The reason is false because stannous chloride is not a powerful oxidizing agent; it is a reducing agent.

6. **Final Answer**:
- Therefore, the correct option is **C**: The assertion is true, but the reason is false.