For the reaction,
`PCl_(5(g))hArrPCl_(3(g))+Cl_(2(g))`, the forward reaction at constant temperature is favoured by:

Options

A. a. introducing an inert gas at constant volume
B. b.introducing `Cl_(2)` at constant volume
C. c. introducing `PCl_(5)` at constant volume
D. d. reducing the volume of the container.

Explanation

To determine the conditions that favor the forward reaction of the equilibrium:

\[ PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g) \]

we will analyze each option provided in the question.

### Step-by-Step Solution

1. **Understanding the Reaction**:
The reaction involves the equilibrium between phosphorus pentachloride (PCl5) and its products, phosphorus trichloride (PCl3) and chlorine gas (Cl2).

2. **Le Chatelier's Principle**:
According to Le Chatelier's principle, if a change is made to a system at equilibrium, the system will adjust to counteract that change and restore a new equilibrium.

3. **Analyzing Each Option**:
- **Option A: Introducing an inert gas at constant volume**:
- When an inert gas is added at constant volume, the total pressure increases, but the partial pressures of the reactants and products remain unchanged. Therefore, there is no effect on the equilibrium position. This option does not favor the forward reaction.

- **Option B: Introducing Cl2 at constant volume**:
- Adding Cl2 increases its concentration. According to Le Chatelier's principle, the equilibrium will shift to the left (backward direction) to reduce the concentration of Cl2. This option does not favor the forward reaction.

- **Option C: Introducing PCl5 at constant volume**:
- Adding PCl5 increases its concentration. The equilibrium will shift to the right (forward direction) to consume the added PCl5. This option favors the forward reaction.

- **Option D: Reducing the volume of the container**:
- Reducing the volume increases the concentration of all gases in the reaction. The equilibrium will shift to the side with fewer moles of gas to counteract the change. In this case, the left side (PCl5) has 1 mole, while the right side has 2 moles (PCl3 + Cl2). Therefore, the equilibrium will shift to the left (backward direction). This option does not favor the forward reaction.

4. **Conclusion**:
The only condition that favors the forward reaction is **Option C: Introducing PCl5 at constant volume**.

### Final Answer:
**The forward reaction at constant temperature is favored by introducing PCl5 at constant volume.**

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