For a phase change:
`H_(2)O(l)hArrH_(2)O(s)`
`0^(@)C`, 1 bar

Options

A. `DeltaG =0`
B. `DeltaS =0`
C. `DeltaH =0` and `DeltaS lt 0`
D. `DeltaU =0`

Explanation

To solve the problem regarding the phase change of water from liquid to solid at 0°C and 1 bar, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Phase Change**: The given reaction is:
\[ H_2O(l) \rightleftharpoons H_2O(s) \]
This indicates a phase change from liquid water to solid ice.

2. **Understand Equilibrium Conditions**: The phase change is at equilibrium, which means that the rate of the forward reaction (liquid to solid) is equal to the rate of the reverse reaction (solid to liquid).

3. **Apply Thermodynamic Principles**: At equilibrium, the change in Gibbs free energy (\( \Delta G \)) for the process is zero. This is a fundamental principle of thermodynamics for equilibrium processes.

4. **State the Standard Conditions**: The problem specifies that this equilibrium occurs at standard conditions, which are defined as:
- Temperature: \( 0^\circ C \)
- Pressure: \( 1 \, \text{bar} \)

5. **Conclude the Gibbs Free Energy Change**: Since the system is at equilibrium under standard conditions, we can conclude:
\[ \Delta G = 0 \]

### Final Answer:
Thus, the correct option is:
\[ \Delta G = 0 \]