In which of the following changes at constant pressure, is work done by system on surrounding ?

Options

A. `H_(2)O(g) rarr H_(2)O(l)`
B. `H_(2)O(s) rarr H_(2)O(l)`
C. `H_(2)O(s) rarr H_(2)O(g)`
D. `H_(2)O(g) rarr H_(2)O(s)`

Explanation

To determine in which of the following changes at constant pressure work is done by the system on the surroundings, we need to analyze each option based on the concept of work done during expansion and contraction of a system.

### Step-by-Step Solution:

1. **Understanding Work Done**:
- Work done by the system on the surroundings occurs during expansion. When a system expands, it pushes against the surrounding atmosphere, doing work on it.

2. **Analyzing the Options**:
- We have four options to evaluate. We need to check whether each change involves an increase in volume (expansion) or a decrease in volume (contraction).

3. **Option A: Water in Gaseous State to Water in Liquid State**:
- This change involves condensation, where gas (water vapor) converts to liquid (water).
- During this process, the volume decreases.
- **Conclusion**: No work is done by the system on the surroundings. (Not the correct option)

4. **Option B: Solid to Liquid**:
- This change involves melting, where a solid (ice) converts to a liquid (water).
- The volume does increase slightly, but the difference in volume between solid and liquid is negligible.
- **Conclusion**: Work done is minimal and not significant enough to be considered. (Not the correct option)

5. **Option C: Solid to Gaseous State**:
- This change involves sublimation, where a solid (like dry ice) converts directly to a gas.
- The volume increases significantly as gases occupy much more volume than solids.
- **Conclusion**: This is an expansion process, and work is done by the system on the surroundings. (This is the correct option)

6. **Option D: Gas to Solid**:
- This change involves deposition, where a gas (like water vapor) converts directly to a solid (like frost).
- The volume decreases as the gas turns into a solid.
- **Conclusion**: No work is done by the system on the surroundings. (Not the correct option)

### Final Answer:
The correct answer is **Option C: Solid to Gaseous State**.