A: The energy gap `Delta_(t)=(4)/(9)Delta_(0)`
R: `Delta_(0)` is always greater than `Delta_(t)`, for same metal ion and ligand.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. ) If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the energy gap \( \Delta_t = \frac{4}{9} \Delta_0 \).
- This is a known relationship in coordination chemistry where \( \Delta_t \) is the splitting energy for tetrahedral complexes and \( \Delta_0 \) is the splitting energy for octahedral complexes.

2. **Understanding the Reason (R)**:
- The reason states that \( \Delta_0 \) is always greater than \( \Delta_t \) for the same metal ion and ligand.
- This is also true, as tetrahedral complexes typically have a smaller splitting energy compared to octahedral complexes. The relationship can be expressed as \( \Delta_t = \frac{2}{3} \Delta_0 \), which implies \( \Delta_0 > \Delta_t \).

3. **Evaluating the Assertion**:
- The assertion is correct because it accurately describes the relationship between the tetrahedral and octahedral splitting energies.

4. **Evaluating the Reason**:
- The reason is also correct as it states that \( \Delta_0 \) is greater than \( \Delta_t \).

5. **Conclusion**:
- While both the assertion and reason are correct, the reason does not provide a correct explanation for the assertion. The assertion is a specific quantitative relationship, while the reason is a general statement about the relative sizes of the splitting energies.

### Final Answer:
- The correct option is **B**: Both A and R are correct, but R is not the correct explanation of A.