When a catalyst is used an equilibrium process,

Options

A. it increases the rate of forward reaction
B. it decreases the rate of backward reaction
C. it decreases activation energy of forward process and decreases activation energy of backward process
D. it fastens the attainment of equilibrium by lowering activation energy.

Explanation

To solve the question regarding the effect of a catalyst on an equilibrium process, we will analyze the options provided and understand the role of a catalyst in chemical reactions.

### Step-by-Step Solution:

1. **Understanding the Role of a Catalyst**:
A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It achieves this by lowering the activation energy required for the reaction to occur.

2. **Effect on Forward and Backward Reactions**:
When a catalyst is introduced in an equilibrium process, it does not favor either the forward or the backward reaction. Instead, it accelerates both reactions equally. This means that the rates of the forward and backward reactions increase, allowing the system to reach equilibrium faster.

3. **Activation Energy**:
A catalyst lowers the activation energy for both the forward and backward reactions. This means that the energy barrier that must be overcome for the reaction to proceed is reduced, facilitating a quicker transition to equilibrium.

4. **Equilibrium Attainment**:
The presence of a catalyst does not change the position of the equilibrium; it only helps the system to reach equilibrium more quickly. Therefore, the catalyst sustains the attainment of equilibrium by lowering the activation energy for both processes.

5. **Evaluating the Options**:
- **Option 1**: "It increases the rate of the forward reaction." - Incorrect, as it increases the rate of both reactions.
- **Option 2**: "It decreases the rate of backward reaction." - Incorrect, as it does not decrease the rate of any reaction.
- **Option 3**: "It decreases activation energy of forward process and decreases activation energy of backward process." - Incorrect, as it lowers the activation energy for both processes but does not specify that it affects them individually.
- **Option 4**: "It sustains the attainment of equilibrium by lowering the activation energy." - Correct, as it accurately describes the role of a catalyst in an equilibrium process.

6. **Conclusion**:
The correct answer is **Option 4**: "It sustains the attainment of equilibrium by lowering the activation energy."