Assertion :- At constant temp `0^(@)C` and 1 atm, the change `H_(2)O(s)rarr H_(2)O(l)Delta H` and `Delta E` both are zero.
Reason :- During isothermal process H and E both remains constant.

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.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
The assertion states that at a constant temperature of \(0^\circ C\) and 1 atm pressure, the change in enthalpy (\(\Delta H\)) and the change in internal energy (\(\Delta E\)) for the phase change from solid water (ice) to liquid water (water) is zero.

- At \(0^\circ C\) and 1 atm, water is at its melting/freezing point. This means that ice and liquid water can coexist in equilibrium.
- At equilibrium, the system does not undergo any net change, hence \(\Delta H = 0\) and \(\Delta E = 0\).

2. **Understanding the Reason**:
The reason states that during an isothermal process, both enthalpy (H) and internal energy (E) remain constant.

- An isothermal process is defined as one that occurs at a constant temperature. In such a process, if there is no net heat exchange or work done, the internal energy change (\(\Delta E\)) and enthalpy change (\(\Delta H\)) can also be zero.
- However, the reason does not specifically relate to the assertion about the phase change of water at equilibrium.

3. **Conclusion**:
- Both the assertion and the reason are true.
- However, the reason does not correctly explain the assertion since the assertion specifically refers to the equilibrium condition of the phase change of water, while the reason discusses isothermal processes in general.

### Final Answer:
The correct option is that both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

---