During the melting of a slab of ice at 273K at atmospheric pressure,

Options

A. positive work is done by the ice water system on the atmosphere
B. positive work is done on the ice water system by the atmosphere
C. the internal energy of the ice water system increases
D. the internal energy of the ice water system decreases.

Explanation

To solve the problem regarding the melting of a slab of ice at 273 K at atmospheric pressure, we need to analyze the statements provided and determine their validity based on the principles of thermodynamics and calorimetry.

### Step-by-Step Solution:

1. **Understanding the System**:
- We have a slab of ice at 273 K (0°C) which is melting. The process occurs at atmospheric pressure.

2. **Analyzing Work Done**:
- **Statement A**: "Positive work is done by the ice water system on the atmosphere."
- When the ice melts, it does not expand against the atmosphere; instead, the volume decreases as it transitions from solid to liquid. Therefore, this statement is **false**.

- **Statement B**: "Positive work is done on the ice water system by the atmosphere."
- Since the atmospheric pressure is acting on the melting ice, and the volume of the ice decreases, the work done by the atmosphere on the system is indeed positive. This statement is **true**.

3. **Internal Energy Considerations**:
- **Statement C**: "The internal energy of the ice water system increases."
- During melting, the system absorbs heat (latent heat of fusion) from the surroundings. Since the system is gaining energy (both in the form of heat and work), the internal energy increases. This statement is **true**.

- **Statement D**: "The internal energy decreases."
- This statement contradicts the previous analysis. Since the system is gaining energy, this statement is **false**.

4. **Conclusion**:
- Based on the analysis, the correct statements are:
- Statement B is true: Positive work is done on the ice water system by the atmosphere.
- Statement C is true: The internal energy of the ice water system increases.

### Final Answer:
The correct options are B and C.

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