Which of the following statements is (are) true ?

Options

A. The concentration of a homogeneous catalyst may appear in the rate expression.
B. A catalyst is always consumed in the reaction.
C. A catalyst must always be in the same phase as the reactants.
D. None of these

Explanation

To determine which of the statements regarding catalysts is true, let's analyze each option step by step.

### Step 1: Analyze Option 1
**Statement:** The concentration of a homogeneous catalyst may appear in the rate expression.

**Explanation:** This statement is true. In reactions involving homogeneous catalysts (catalysts that are in the same phase as the reactants), the concentration of the catalyst can indeed appear in the rate expression. This is because the rate of reaction can depend on the concentration of all species present in the same phase.

### Step 2: Analyze Option 2
**Statement:** A catalyst is always consumed in the reaction.

**Explanation:** This statement is false. A catalyst is defined as a substance that increases the rate of a reaction without being consumed in the process. It may participate in the reaction mechanism but is regenerated by the end of the reaction.

### Step 3: Analyze Option 3
**Statement:** A catalyst must always be in the same phase as the reactants.

**Explanation:** This statement is also false. A catalyst can be either homogeneous (in the same phase as the reactants) or heterogeneous (in a different phase from the reactants). Therefore, it is not necessary for a catalyst to be in the same phase as the reactants.

### Step 4: Analyze Option 4
**Statement:** None of these.

**Explanation:** Since we have determined that Option 1 is true, this statement is false.

### Conclusion
Based on the analysis:
- **True Statement:** Option 1 (The concentration of a homogeneous catalyst may appear in the rate expression).
- **False Statements:** Options 2, 3, and 4.

### Final Answer
The correct option is **Option 1**.

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