Assertion : `Ce^(4+)` is good analytical reagent.
Reason: `Ce^(4+)` has the tendency to change to `Ce^(3+)`

Options

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

Answer

To solve the assertion and reason question regarding `Ce^(4+)`, we will analyze both the assertion and the reason step by step.

### Step-by-Step Solution

1. **Understanding the Assertion**:
- The assertion states that `Ce^(4+)` is a good analytical reagent.
- An analytical reagent is a substance that is used in chemical analysis and must have a high standard of purity.

2. **Properties of `Ce^(4+)`**:
- Cerium (Ce) has an atomic number of 58. Its electronic configuration is `[Xe] 4f^1 5d^1 6s^2`.
- When cerium loses four electrons to form `Ce^(4+)`, its electronic configuration becomes `[Xe] 4f^0`, which is a noble gas configuration. This indicates that `Ce^(4+)` is stable.

3. **Reduction Potential**:
- The reduction potential for the conversion of `Ce^(4+)` to `Ce^(3+)` is +1.74 V, which is a positive value.
- A positive reduction potential indicates that the reaction is favorable and that `Ce^(4+)` can be reduced to `Ce^(3+)` when a reducing agent is present.

4. **Kinetic Stability**:
- The noble gas configuration of `Ce^(4+)` provides it with sufficient kinetic stability. However, the positive reduction potential indicates that it can easily be reduced to `Ce^(3+)` in the presence of a reducing agent.

5. **Conclusion on Assertion**:
- Since `Ce^(4+)` has a noble gas configuration and a positive reduction potential, it is indeed a good analytical reagent. Thus, the assertion is correct.

6. **Understanding the Reason**:
- The reason states that `Ce^(4+)` has a tendency to change to `Ce^(3+)`.
- This is true because of the positive reduction potential, which indicates that `Ce^(4+)` can be reduced to `Ce^(3+)` when a reducing agent is present.

7. **Conclusion on Reason**:
- The reason correctly explains why `Ce^(4+)` is a good analytical reagent, as it highlights the stability of `Ce^(3+)` compared to `Ce^(4+)`.

8. **Final Conclusion**:
- Both the assertion and the reason are correct, and the reason is a correct explanation for the assertion.

### Final Answer:
Both assertion and reason are true, and the reason is the correct explanation for the assertion.