The following two reactions:
i. `PCl_(5)(g) hArr PCl_(3)(g)+Cl_(2)(g)`
(ii) `COCl_(2)(g) hArr CO(g)+Cl_(2)(g)`
are simultaneously in equilibrium in a container at constant volume. A few moles of `CO(g)` are later introduced into the vessel. After some time, the new equilibrium concentration of

Options

A. `PCl_(5)` will remain unchanged
B. `Cl_(2)` will be greater
C. `PCl_(5)` will become greater
D. `PCl_(5)` will become less

Explanation

To solve the problem regarding the simultaneous equilibrium of the two reactions and the effect of adding CO gas, we will follow these steps:

### Step 1: Understand the Initial Equilibrium
We have two reactions occurring simultaneously in a closed container:
1. \( PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g) \)
2. \( COCl_2(g) \rightleftharpoons CO(g) + Cl_2(g) \)

At the initial state, both reactions are at equilibrium, meaning the rates of the forward and reverse reactions are equal.

### Step 2: Introduce CO into the System
When a few moles of \( CO(g) \) are introduced into the vessel, the concentration of \( CO \) increases. This disturbance will affect the equilibrium of the second reaction.

### Step 3: Apply Le Chatelier's Principle
According to Le Chatelier's Principle, if a system at equilibrium is disturbed by changing the concentration of a reactant or product, the system will shift in the direction that counteracts the change. Here, since \( CO \) is a product in the second reaction, increasing its concentration will shift the equilibrium to the left (the reverse direction) to reduce the concentration of \( CO \).

### Step 4: Analyze the Effect on the Second Reaction
As the equilibrium of the second reaction shifts to the left:
- The concentration of \( COCl_2(g) \) will increase.
- The concentration of \( Cl_2(g) \) will decrease.

### Step 5: Analyze the Effect on the First Reaction
The decrease in \( Cl_2(g) \) will affect the first reaction. Since \( Cl_2 \) is a product in the first reaction, a decrease in its concentration will shift the equilibrium of the first reaction to the right (the forward direction) to produce more \( Cl_2 \).

### Step 6: Determine the Final Effect on \( PCl_5 \)
As the first reaction shifts to the right:
- The concentration of \( PCl_5(g) \) will decrease.
- The concentrations of \( PCl_3(g) \) and \( Cl_2(g) \) will increase.

### Conclusion
The final effect of introducing \( CO(g) \) into the system is that the concentration of \( PCl_5(g) \) decreases.

### Summary of Steps:
1. Identify the initial equilibrium state of both reactions.
2. Introduce \( CO(g) \) into the system.
3. Apply Le Chatelier's Principle to determine the shift in equilibrium for the second reaction.
4. Analyze the impact on the first reaction due to the change in \( Cl_2(g) \).
5. Conclude the effect on the concentration of \( PCl_5(g) \).