Assertion (A): Cerium (Ce) exhibits +4 oxidation state.
Reason (R): `Ce^(4+)` has `4f^4` electronic configuration which is less stable.

Options

A. Both A and Rare true and R is the correct explanation of A.
B. Both A and R are true but R is NOT the correct explanation of A.
C. A is true but R is false.
D. A is false and R is True

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that Cerium (Ce) exhibits a +4 oxidation state.
- Cerium is a lanthanide element with an atomic number of 58. Its electronic configuration is [Xe] 4f^1 5d^1 6s^2.
- Cerium can lose electrons from its outermost orbitals (6s and 5d) and also from the 4f orbital, allowing it to exhibit a +4 oxidation state.

2. **Understanding the Reason (R)**:
- The reason states that `Ce^(4+)` has a 4f^4 electronic configuration which is less stable.
- When Cerium loses 4 electrons to form `Ce^(4+)`, it actually loses 2 electrons from the 6s orbital and 2 electrons from the 5d orbital, resulting in the electronic configuration of `Ce^(4+)` being [Xe] (which is the stable noble gas configuration).
- Therefore, the statement that `Ce^(4+)` has a 4f^4 configuration is incorrect. In fact, `Ce^(4+)` does not have any 4f electrons left, as they are not involved in the +4 oxidation state.

3. **Conclusion**:
- The assertion is true: Cerium does exhibit a +4 oxidation state.
- The reason is false: `Ce^(4+)` does not have a 4f^4 configuration and is not less stable; it actually achieves a stable noble gas configuration.

### Final Answer:
- Assertion (A) is true, and Reason (R) is false. Therefore, the correct option is that the assertion is correct, but the reason is incorrect.

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