Assertion :- Oxidation number of Cr in `Cr(CO)_(6)` is zero.
Reason :- Cr is a metal.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

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

**Assertion:** The oxidation number of Cr in `Cr(CO)_(6)` is zero.
**Reason:** Cr is a metal.

### Step-by-Step Solution:

1. **Understanding the Compound:**
- The compound in question is `Cr(CO)_(6)`, which is a coordination complex where chromium (Cr) is surrounded by six carbon monoxide (CO) ligands.

2. **Identifying the Nature of CO:**
- Carbon monoxide (CO) is a neutral ligand, meaning it does not carry any charge. Therefore, it does not contribute to the overall charge of the complex.

3. **Setting Up the Oxidation Number Equation:**
- Let the oxidation number of chromium (Cr) be represented as \( x \).
- Since there are six CO ligands, the contribution from them is \( 6 \times 0 = 0 \) (because CO is neutral).
- The overall charge of the complex `Cr(CO)_(6)` is also neutral (0).

4. **Formulating the Equation:**
- The equation based on the oxidation states can be written as:
\[ x + 6(0) = 0 \]
- Simplifying this gives:
\[ x = 0 \]

5. **Conclusion on the Oxidation Number:**
- Therefore, the oxidation number of chromium in `Cr(CO)_(6)` is indeed 0, confirming the assertion is correct.

6. **Evaluating the Reason:**
- The reason states that "Cr is a metal." While it is true that chromium is a metal, this fact does not explain why the oxidation number of Cr in this specific complex is zero.
- The oxidation state is determined by the charge contributions from the ligands, not merely by the fact that Cr is a metal.

7. **Final Evaluation:**
- Both the assertion and the reason are true, but the reason does not correctly explain the assertion. Thus, the correct answer is that both are true, but the reason is not a correct explanation of the assertion.

### Final Answer:
**Option B:** Both assertion and reason are true, but reason is not a correct explanation of the assertion.

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