Which of the following are the correct :

Options

A. A Catalyst remains unchanged in mass and chemical compositions at the end of reactions.
B. Finely divided state of catalyst is more efficient for the reaction
C. Catalyst change equilibrium state of the reaction
D. A catalyst changes the entropy and the free energy of a reaction

Explanation

To solve the question regarding the correctness of the statements about catalysts, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: A catalyst remains unchanged in mass and chemical properties at the end of the reaction.**
- **Analysis**: A catalyst is a substance that increases the rate of a chemical reaction without undergoing any permanent change itself. At the end of the reaction, the catalyst can be recovered in its original form, meaning its mass and chemical properties remain unchanged.
- **Conclusion**: This statement is **correct**.

2. **Statement 2: The finely divided state of a catalyst is more effective for the reaction.**
- **Analysis**: The effectiveness of a catalyst is often related to its surface area. A finely divided catalyst has a larger surface area compared to a bulk catalyst, allowing more active sites for the reaction to occur. This increases the catalytic efficiency.
- **Conclusion**: This statement is **correct**.

3. **Statement 3: A catalyst changes the equilibrium state of the reaction.**
- **Analysis**: A catalyst does not change the position of equilibrium in a chemical reaction. It only speeds up the rate at which equilibrium is reached. The concentrations of reactants and products at equilibrium remain the same regardless of the presence of a catalyst.
- **Conclusion**: This statement is **incorrect**.

4. **Statement 4: A catalyst changes the entropy and the free energy of a reaction.**
- **Analysis**: A catalyst affects the rate of a reaction but does not change the thermodynamic properties such as entropy and free energy. The overall energy change (ΔG) and entropy change (ΔS) of the reaction remain the same regardless of the presence of a catalyst.
- **Conclusion**: This statement is **incorrect**.

### Final Summary:
- **Correct Statements**: Statement 1 and Statement 2.
- **Incorrect Statements**: Statement 3 and Statement 4.