Which of the following statement 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 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, we will analyze each statement one by one.

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

- A homogeneous catalyst is one that is in the same phase as the reactants. In many reactions, the concentration of a catalyst can indeed appear in the rate expression, even though it is not consumed in the reaction. Therefore, this statement is **true**.

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

- This statement is **false**. By definition, a catalyst is a substance that increases the rate of a reaction without being consumed in the process. Therefore, it can participate in the reaction mechanism but is regenerated at the end.

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

- This statement is also **false**. While a homogeneous catalyst is in the same phase as the reactants, a heterogeneous catalyst can be in a different phase. For example, in the Haber process, nitrogen and hydrogen are gases, while iron (a catalyst) is a solid. Therefore, it is not necessary for a catalyst to be in the same phase as the reactants.

### Step 4: Analyze the fourth statement
**Statement 4:** None of these.

- Since we have determined that the first statement is true and the others are false, this statement is also **false**.

### Conclusion
The only true statement is:
- **Statement 1:** The concentration of a homogeneous catalyst may appear in the rate expression.

### Final Answer
The correct answer is: **Statement 1 is true.**

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