In a vessel `N_(2),H_(2)andNH_(3)` are at equilibrium. Some helium gas is introduction into the vessel so that total pressure increases while temperature and volume remain constant. According to Le Chatelier's principle, the dissociation of `NH_(3)` (A)increases (B)decreases (C)remains unchanged (D)equilibrium is disturbed

Options

A. increases
B. decreases
C. remains unchanged
D. equilibrium is disturbed.

Explanation

To solve the problem, we need to understand the implications of adding an inert gas (helium) to a system at equilibrium, while keeping the temperature and volume constant.

### Step-by-Step Solution:

1. **Identify the Reaction**:
The dissociation of ammonia can be represented by the following balanced chemical equation:
\[ 2NH_3(g) \rightleftharpoons N_2(g) + 3H_2(g) \]

2. **Understand the Effect of Inert Gas**:
When an inert gas like helium is added to the system at constant volume, it does not react with the components of the equilibrium. The total pressure of the system increases, but the partial pressures of the reactants and products remain unchanged because the volume is constant.

3. **Apply Le Chatelier's Principle**:
Le Chatelier's principle states that if an external change is applied to a system at equilibrium, the system will adjust to counteract that change and restore a new equilibrium. However, in this case, since the volume is constant, the addition of helium does not change the concentrations (or partial pressures) of the reactants and products.

4. **Conclusion**:
Since the addition of helium does not affect the equilibrium concentrations of \(N_2\), \(H_2\), and \(NH_3\), the dissociation of \(NH_3\) remains unchanged. Therefore, the correct answer is:
\[ \text{(C) remains unchanged} \]

### Final Answer:
The dissociation of \(NH_3\) remains unchanged when helium gas is introduced at constant volume.

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