Assertion : In high spin situation, configuration of ` d^5 ` ions will be `t_(2g)^3e_g^2 `
Reason : In high spin situation pairing energy is less than crystal field energy.

Options

A. a. if both assertion and reason are true and reason is thr correct explanation of assertion
B. b. If both assertion and reason are true but reason is not the correct explanation of assertion
C. c. If assertion is true but reason is false
D. d. If both assertion and reson are false.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that in a high spin situation, the configuration of `d^5` ions will be `t_(2g)^3 e_g^2`.
- In an octahedral field, the `d` orbitals split into two groups: `t_(2g)` (lower energy) and `e_g` (higher energy).
- For a `d^5` configuration in a high spin complex, electrons will fill the `t_(2g)` orbitals first and then the `e_g` orbitals, leading to the configuration `t_(2g)^3 e_g^2`.

2. **Understanding the Reason**:
- The reason states that in a high spin situation, pairing energy is less than crystal field energy.
- In reality, for high spin complexes, the pairing energy is greater than the crystal field splitting energy (Δo). This allows electrons to occupy higher energy orbitals without pairing.

3. **Analyzing the Assertion and Reason**:
- The assertion is **true**: The configuration `t_(2g)^3 e_g^2` is indeed correct for a high spin `d^5` ion.
- The reason is **false**: In high spin situations, pairing energy is greater than crystal field energy, not less.

4. **Conclusion**:
- The assertion is true, but the reason is false. Therefore, the correct answer to the question is that the assertion is true, but the reason is not a correct explanation of the assertion.

### Final Answer:
- Assertion: True
- Reason: False