As per Lechatlier's Principle any stress applied on the equilibrium state is minimised by shifting of equilibrium.
In which cases increase in pressure shifts the equilibrium in forward direction?

Options

A. `underset((g))(N_(2)) + underset((g))( O_(2)) hArr underset((g))(2NO)`
B. `N_(2) + 3H_(2) hArr 2NH_(3)`
C. `N_(2)O_(4) hArr 2NO_(2)`
D. `S_(8) (R) hArr S_(8)`(M)

Answer

To determine in which cases an increase in pressure shifts the equilibrium in the forward direction according to Le Chatelier's Principle, we can follow these steps:

### Step 1: Understand Le Chatelier's Principle
Le Chatelier's Principle states that if an external change (stress) is applied to a system at equilibrium, the system will adjust to counteract that change and restore a new equilibrium.

### Step 2: Analyze the Effect of Pressure
When pressure is increased in a system involving gases, the equilibrium will shift towards the side with fewer moles of gas. This is because the system will try to reduce the pressure by favoring the side with less volume (fewer moles).

### Step 3: Examine the Given Reactions
We need to analyze the provided reactions to see how many moles of gas are present on both sides (reactants vs. products).

1. **Reaction 1:** A + B ⇌ C + D
- Total moles of reactants = 2
- Total moles of products = 2
- **Effect of pressure:** No shift (equal moles).

2. **Reaction 2:** N2 + 3H2 ⇌ 2NH3
- Total moles of reactants = 4
- Total moles of products = 2
- **Effect of pressure:** Forward shift (fewer moles of products).

3. **Reaction 3:** N2O4 ⇌ 2NO2
- Total moles of reactants = 1
- Total moles of products = 2
- **Effect of pressure:** Backward shift (more moles of products).

4. **Reaction 4:** Rhombic sulfur ⇌ Monoclinic sulfur
- This reaction involves solid phases, and pressure has no effect on solids.
- **Effect of pressure:** No shift.

### Step 4: Conclusion
From the analysis, we find that the only reaction where an increase in pressure shifts the equilibrium in the forward direction is the second reaction (N2 + 3H2 ⇌ 2NH3).

### Final Answer
The increase in pressure shifts the equilibrium in the forward direction in the case of the reaction: **N2 + 3H2 ⇌ 2NH3**.

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