Le - Chatelier principle is not applicable to :

Options

A. `H_(2)(g)+I_(2)(g)hArr2HI(g)`
B. `Fe(s)+S(s)hArrFeS(s)`
C. `N_(2)(g)+3H_(2)(g)hArrNH_(3)(g)`
D. `N_(2)(g)+O_(2)(g)hArr2NO(g)`

Answer

To determine where Le Chatelier's principle is not applicable, we need to analyze the given reactions and identify the conditions under which the principle operates. 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.

### Step-by-Step Solution:

1. **Understanding Le Chatelier's Principle**:
- Le Chatelier's principle applies to systems in equilibrium. It indicates how the equilibrium position shifts in response to changes in concentration, pressure, or temperature.

2. **Identifying the Types of Reactions**:
- We need to evaluate the reactions provided in the question to see which ones involve pure solids and which involve gases or solutions.

3. **Analyzing Each Reaction**:
- **Reaction A**: \( H_2(g) + I_2(g) \rightleftharpoons 2 HI(g) \)
- This is a gaseous reaction. Changes in concentration or pressure will affect the equilibrium. Thus, Le Chatelier's principle is applicable here.

- **Reaction B**: \( Fe(s) + S(s) \rightleftharpoons FeS(s) \)
- This is a solid-solid reaction. Adding or removing solids does not change the concentration of solids in equilibrium. Therefore, Le Chatelier's principle is not applicable to this reaction.

- **Reaction C**: \( N_2(g) + 3H_2(g) \rightleftharpoons 2 NH_3(g) \)
- This is also a gaseous reaction. Changes in concentration or pressure will affect the equilibrium, so Le Chatelier's principle is applicable.

- **Reaction D**: (Assuming a gaseous reaction similar to A and C)
- If this is a gaseous reaction, then Le Chatelier's principle would also be applicable here.

4. **Conclusion**:
- From the analysis, we find that Le Chatelier's principle is not applicable to the solid-solid equilibrium represented by Reaction B: \( Fe(s) + S(s) \rightleftharpoons FeS(s) \).

### Final Answer:
Le Chatelier's principle is not applicable to the reaction \( Fe(s) + S(s) \rightleftharpoons FeS(s) \) (Option B).

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