Assertion : All enzymes are not proteins.
Reason : RNA molecules that possess catalytic activity are called ribozymes.

Explanation

To analyze the assertion and reason statements, we will break down the information provided.

### Step 1: Understand the Assertion
The assertion states: "All enzymes are not proteins."
- This means that while many enzymes are proteins, there are exceptions.

### Step 2: Evaluate the Assertion
- It is a fact that the majority of enzymes are proteins, which are made up of amino acids. However, there are enzymes that are not proteins.
- For instance, RNA molecules can also act as enzymes, which leads us to the next part of the question.

### Step 3: Understand the Reason
The reason states: "RNA molecules that possess catalytic activity are called ribozymes."
- Ribozymes are indeed RNA molecules that can catalyze biochemical reactions, similar to how protein enzymes function.

### Step 4: Evaluate the Reason
- This statement is true as ribozymes are recognized for their ability to catalyze reactions, thus supporting the assertion that not all enzymes are proteins.

### Step 5: Conclusion
- Both the assertion and the reason are true statements. Furthermore, the reason correctly explains the assertion.

### Final Answer
- The assertion is true, and the reason is true and provides a correct explanation for the assertion.

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