A : `C_("diamond") rightarrow C_("graphite")`
`Delta H and Delta U` are same for this reaction.
R: Entropy increases during the conversion of diamond to graphite.

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 and 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 is true statement but Reason is false, then mark (3)

Answer

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

### Step 1: Analyze the Assertion (A)
The assertion states that the enthalpy change (ΔH) and the internal energy change (ΔU) are the same for the reaction:
\[ \text{C (diamond)} \rightarrow \text{C (graphite)} \]

**Explanation:**
- The relationship between ΔH and ΔU is given by the equation:
\[ \Delta H = \Delta U + \Delta n_g RT \]
where \( \Delta n_g \) is the change in the number of moles of gas.
- In this reaction, there are no gaseous reactants or products, which means \( \Delta n_g = 0 \).
- Therefore, the equation simplifies to:
\[ \Delta H = \Delta U \]
- This confirms that the assertion is true.

### Step 2: Analyze the Reason (R)
The reason states that entropy increases during the conversion of diamond to graphite.

**Explanation:**
- Diamond has a more ordered structure due to its tetrahedral arrangement of carbon atoms, forming a strong covalent network.
- Graphite, on the other hand, has a layered structure with weaker van der Waals forces between the layers, making it less ordered.
- As a result, the transition from diamond to graphite leads to an increase in disorder, which corresponds to an increase in entropy (ΔS > 0).

### Step 3: Conclusion
- The assertion (A) is true: ΔH and ΔU are the same for the reaction.
- The reason (R) is also true: Entropy increases during the conversion of diamond to graphite.

### Final Statement
Both the assertion and the reason are true, but the reason does not explain the assertion.