Which of the followig equilibrium will shift in forward direction on increase of pressure?

Options

A. `S_("solid")hArrS_("liquid")`
B. `H_(2)O_(ice)hArrH_(2)O(l)`
C. `Ga_(s)hArrGa_(("liquid"))`
D. Both 2 & 3

Answer

To determine which equilibrium will shift in the forward direction upon an increase in pressure, we need to analyze the given equilibria based on the concept of Le Chatelier's principle. This principle states that if an external change is applied to a system at equilibrium, the system will adjust to counteract that change.

### Step-by-Step Solution:

1. **Identify the Equilibria**: The question provides three equilibria:
- S (solid) ⇌ S (liquid)
- H2O (ice) ⇌ H2O (liquid)
- Gallium (solid) ⇌ Gallium (liquid)

2. **Understand the Effect of Pressure**: According to Le Chatelier's principle, increasing pressure will favor the side of the equilibrium that has fewer moles of gas or, in the case of solids and liquids, the side with a smaller volume.

3. **Analyze Each Equilibrium**:
- **First Equilibrium (S ⇌ S)**: This equilibrium involves solid and liquid states of the same substance. Generally, liquids have a higher volume than solids. Therefore, increasing pressure would shift the equilibrium towards the solid side (backward direction).

- **Second Equilibrium (H2O (ice) ⇌ H2O (liquid))**: Ice (solid) has a lower density than liquid water. When pressure is increased, the equilibrium will shift towards the liquid state because the liquid has a higher density and occupies less volume compared to ice. Thus, this equilibrium shifts in the forward direction.

- **Third Equilibrium (Gallium (solid) ⇌ Gallium (liquid))**: Similar to the first equilibrium, gallium in its liquid state has a larger volume than in its solid state. Therefore, increasing pressure would shift this equilibrium towards the solid state (backward direction).

4. **Conclusion**: Based on the analysis, the only equilibrium that shifts in the forward direction upon an increase in pressure is the second one: H2O (ice) ⇌ H2O (liquid).

### Final Answer:
The equilibrium that will shift in the forward direction on an increase of pressure is **H2O (ice) ⇌ H2O (liquid)**.