Phosphorous pentachloride when heated in a sealed tube at `700 K` it undergoes decomposition as
`PCl_(5)(g) hArr PCl_(3)(g)+Cl_(2)(g), K_(p)=38` atm
Vapour density of the mixture is `74.25`.
When an inert gas is added to the given reversible process, then the equilibrium will.

Options

A. Be unaffected
B. Shift in backward direction
C. Shift in forward direction
D. Cannot be predicted

Explanation

To solve the problem regarding the effect of adding an inert gas to the equilibrium of the decomposition of phosphorus pentachloride (PCl5), we can follow these steps:

### Step 1: Understand the Reaction
The decomposition reaction is given as:
\[ PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g) \]

### Step 2: Identify the Equilibrium Constant
The equilibrium constant \( K_p \) for the reaction is provided as \( K_p = 38 \) atm. This value indicates the ratio of the partial pressures of the products to the reactants at equilibrium.

### Step 3: Analyze the Effect of Adding an Inert Gas
When an inert gas is added to a system at equilibrium, its effect depends on the conditions under which it is added:

- **At Constant Volume**: The addition of an inert gas does not change the partial pressures of the reactants and products because the volume remains constant. Therefore, the equilibrium position remains unaffected.

- **At Constant Pressure**: The addition of an inert gas increases the total volume of the system. This results in a decrease in the partial pressures of the reactants and products. According to Le Chatelier's principle, the equilibrium will shift in the direction that increases the number of moles of gas to counteract the change.

### Step 4: Determine the Change in Moles
For the given reaction:
- On the reactant side, there is 1 mole of \( PCl_5 \).
- On the product side, there are 1 mole of \( PCl_3 \) and 1 mole of \( Cl_2 \), totaling 2 moles.

Thus, when the inert gas is added at constant pressure, the equilibrium will shift to the right (toward the products) because the number of moles increases from 1 to 2.

### Conclusion
Since the effect of adding an inert gas depends on whether the volume is constant or the pressure is constant, we conclude that:

- If the inert gas is added at constant volume, the equilibrium is unaffected.
- If the inert gas is added at constant pressure, the equilibrium shifts to the right (toward products).

Thus, the answer to the question is: **The equilibrium will shift in the forward direction (to the right)** if the inert gas is added at constant pressure.