Which of the following is not a physical equilibrium ?

Options

A. `Ice rarr Water`
B. `I_(2)(s) rarr I_(2)(g)`
C. `S(l) rarr S(g)`
D. `3O_(2)(g) rarr 2O_(3)(g)`

Explanation

To determine which of the given options is not a physical equilibrium, we need to understand the concept of equilibrium and specifically physical equilibrium.

### Step-by-Step Solution:

1. **Define Equilibrium**:
- Equilibrium is a state in a chemical reaction where the concentrations of reactants and products remain constant over time. This occurs when the rate of the forward reaction equals the rate of the backward reaction.

2. **Understand Physical Equilibrium**:
- Physical equilibrium occurs between different phases of the same substance, where there is no change in chemical composition. It involves changes in physical states (solid, liquid, gas) without altering the chemical identity of the substance.

3. **Analyze the Options**:
- **Option 1**: Ice converting into water (solid to liquid).
- This is a phase change from solid to liquid, with no change in chemical composition (both are forms of water). This represents physical equilibrium.

- **Option 2**: Solid iodine converting into gaseous iodine.
- This is a phase change from solid to gas, again with no change in chemical composition (both are forms of iodine). This represents physical equilibrium.

- **Option 3**: Liquid sulfur converting into gaseous sulfur.
- This is a phase change from liquid to gas, with no change in chemical composition (both are forms of sulfur). This represents physical equilibrium.

- **Option 4**: Oxygen converting into ozone.
- This involves a chemical change where molecular oxygen (O₂) is transformed into ozone (O₃). There is no phase change, and the chemical composition is altered. This does not represent physical equilibrium.

4. **Conclusion**:
- The option that is not a physical equilibrium is **Option 4: Oxygen converting into ozone**.

### Final Answer:
**Option 4: Oxygen converting into ozone is not a physical equilibrium.**