Which is not the correct statement for a catalyst?

Options

A. It does not alter `E_(a)` .
B. The surface of a catalyst adsorbs reactant
C. Catalyst may form intermediates with reactants.
D. Action of enzyme catalyst is always specific.

Answer

To determine which statement about a catalyst is incorrect, we need to analyze the properties and functions of catalysts. Let's go through the statements one by one.

### Step-by-Step Solution:

1. **Definition of a Catalyst**:
A catalyst is defined as a substance that alters the rate of a chemical reaction without being consumed in the process. It achieves this by providing an alternative pathway for the reaction with a lower activation energy.

2. **Analyzing the Statements**:
- **Statement A**: "A catalyst does not alter activation energy."
- This statement is **incorrect**. A catalyst does alter the activation energy of a reaction, typically lowering it to increase the reaction rate.

- **Statement B**: "The surface of a catalyst adsorbs the reactant."
- This statement is **correct**. According to the adsorption theory of catalysis, the reactants are adsorbed onto the surface of the catalyst, which facilitates the reaction.

- **Statement C**: "A catalyst may form intermediates with a reactant."
- This statement is **correct**. Catalysts can form temporary intermediates with reactants, which helps in providing a pathway with lower activation energy.

- **Statement D**: "The action of enzyme catalysts is always specific."
- This statement is **correct**. Enzymes are biological catalysts that are specific to particular reactions or types of substrates.

3. **Conclusion**:
Based on the analysis, the statement that is not correct for a catalyst is **Statement A**: "A catalyst does not alter activation energy."

### Final Answer:
The incorrect statement about a catalyst is: **A catalyst does not alter activation energy.**

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