Pick out the correct statement from among the four:

Options

A. When a liquid boils work is done on the system
B. In case of Boiling of a liquid `DeltaH= DeltaU`
C. When a liquid boils at its boiling temperature, `Q_(P)= DeltaH`
D. For the process of boiling of a liquid, Q=0

Answer

To solve the question of selecting the correct statement regarding the boiling of a liquid, we will analyze each of the four statements provided.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- Statement: "When a liquid boils, work is done on the system."
- Explanation: When a liquid boils, it expands to become a gas. In this case, the system (the liquid) is doing work on the surroundings as it expands. Therefore, this statement is incorrect.

2. **Analyze the Second Statement:**
- Statement: "In case of boiling of a liquid, ΔH = ΔU."
- Explanation: The relationship between enthalpy change (ΔH) and internal energy change (ΔU) during a phase change can be expressed as:
\[ ΔH = ΔU + ΔnRT \]
where Δn is the change in the number of moles of gas. Since boiling involves a change in phase from liquid to gas, Δn is not zero. Therefore, ΔH is not equal to ΔU, making this statement incorrect.

3. **Analyze the Third Statement:**
- Statement: "When a liquid boils at its boiling temperature, qp = ΔH."
- Explanation: At the boiling point, the heat added to the system (qp) is used for the phase change (boiling) and is equal to the change in enthalpy (ΔH). Therefore, this statement is correct.

4. **Analyze the Fourth Statement:**
- Statement: "For the process of boiling of a liquid, q = 0."
- Explanation: During boiling, heat is absorbed by the liquid to convert it into vapor. Therefore, q is not equal to 0; it is actually positive as heat is being supplied to the system. This statement is incorrect.

### Conclusion:
The correct statement is the **third statement**: "When a liquid boils at its boiling temperature, qp = ΔH."