Assertion `:` All enzymes are proteins but all proteins are not enzymes.
Reason`:` Keratin is an enzyme.

Options

A. Both assertion and reason correct and the reason is correct expansion to assertion.
B. Both assertion and reason are correct but reason is not the correct expansion of assertion.
C. Assertion is correct but reason is wrong
D. Assertion is incorrect but reason is correct.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "All enzymes are proteins, but all proteins are not enzymes." This means that while every enzyme is a type of protein, not every protein functions as an enzyme.

2. **Defining Enzymes**: Enzymes are biological catalysts that speed up biochemical reactions in living organisms. They are typically proteins that have a specific three-dimensional structure allowing them to interact with substrates and facilitate chemical reactions.

3. **Defining Proteins**: Proteins are large biomolecules composed of amino acids. They perform a variety of functions in the body, including structural roles, transport, and immune responses. However, not all proteins have catalytic activity.

4. **Analyzing the Reason**: The reason provided is that "Keratin is an enzyme." We need to evaluate this statement. Keratin is a type of protein found in hair, nails, and skin, primarily serving a structural role.

5. **Evaluating Keratin**: Keratin does not have catalytic properties and does not assist in biochemical reactions. Therefore, the statement that "Keratin is an enzyme" is incorrect.

6. **Conclusion**: The assertion is correct: all enzymes are proteins, but not all proteins are enzymes. The reason is incorrect because keratin is not an enzyme; it is a structural protein.

### Final Answer:
- **Assertion**: True
- **Reason**: False