Le Chatelier's principle is not applicable to

Options

A. `Fe(s)+S(s) hArr FeS(s)`
B. `H_(2)(g)+I_(2)(g) hArr 2HI(g)`
C. `N_(2)(g)+3H_(2)(g) hArr 2NH_(3)(g)`
D. `N_(2)(g)+O_(2)(g) hArr 2NO(g)`

Answer

To determine when Le Chatelier's principle is not applicable, we need to analyze the provided options based on the principle's requirements.

### Step-by-Step Solution:

1. **Understanding Le Chatelier's Principle**: Le Chatelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. This principle applies to both physical and chemical equilibria.

2. **Analyzing the Options**:
- **Option A**: Fe(s) + S(s) ⇌ FeS(s)
- All species are solids. In this case, the concentrations of solids do not change, as their activities are considered to be constant. Therefore, Le Chatelier's principle does not apply.
- **Option B**: H2(g) + I2(g) ⇌ 2HI(g)
- This is a gaseous equilibrium. Changes in concentration, pressure, or temperature can shift the equilibrium, so Le Chatelier's principle applies.
- **Option C**: N2(g) + 3H2(g) ⇌ 2NH3(g)
- This is also a gaseous equilibrium. Similar to option B, changes can affect the equilibrium position, so Le Chatelier's principle applies.
- **Option D**: N2(g) + O2(g) ⇌ 2NO(g)
- This is again a gaseous equilibrium. Changes can affect the equilibrium position, so Le Chatelier's principle applies.

3. **Conclusion**: Since Le Chatelier's principle is not applicable to the equilibrium involving only solids (Option A), we conclude that the correct answer is:
- **Answer**: Option A (Fe(s) + S(s) ⇌ FeS(s))