Assertion : For the change, `H_(2)O_((l))rarr H_(2)O_((s)),DeltaH=DeltaU`.
Reason : No enthalpy change is involved in this process.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

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

**Assertion:** For the change \( H_2O_{(l)} \rightarrow H_2O_{(s)} \), \( \Delta H = \Delta U \).

**Reason:** No enthalpy change is involved in this process.

### Step-by-Step Solution:

1. **Understanding the Terms:**
- \( \Delta H \) represents the change in enthalpy.
- \( \Delta U \) represents the change in internal energy.
- The process in question is the phase change from liquid water to solid ice.

2. **Applying the Enthalpy Equation:**
- The relationship between enthalpy change and internal energy change can be expressed as:
\[ \Delta H = \Delta U + \Delta n_g RT \]
- Here, \( \Delta n_g \) is the change in the number of moles of gaseous products minus the number of moles of gaseous reactants.

3. **Identifying \( \Delta n_g \):**
- In the phase change from liquid to solid, there are no gaseous molecules involved. Thus:
\[ \Delta n_g = 0 \]
- This means that the term \( \Delta n_g RT \) becomes zero.

4. **Substituting into the Enthalpy Equation:**
- Substituting \( \Delta n_g = 0 \) into the enthalpy equation gives:
\[ \Delta H = \Delta U + 0 \]
- Therefore, we find that:
\[ \Delta H = \Delta U \]

5. **Conclusion about the Assertion:**
- Since we have shown that \( \Delta H = \Delta U \) for the phase change from liquid to solid, the assertion is **true**.

6. **Analyzing the Reason:**
- The reason states that "no enthalpy change is involved in this process." This is incorrect because there is indeed an enthalpy change associated with the phase transition (the latent heat of fusion).
- The correct statement would be that the volume change is negligible, which leads to \( \Delta H \) being equal to \( \Delta U \).

7. **Final Evaluation:**
- The assertion is true, but the reason is false. Therefore, the correct conclusion is that the assertion is true, but the reason is false.

### Final Answer:
- The assertion is true, and the reason is false.