Assertion (A ) : Bt' in Bt toxin represent Bacillus thuringiensis.
Reason (R ) : Bt toxin is produced by a virus.

Options

A. Both assertion (A) and reason (R ) are true and reason (R ) is the correct explanation of assertion (A ) .
B. Both assertion (A) and reason ( R) are true but reason (R ) is not the correct explaination of assertion (A ) .
C. Assertion (A) is true but reason (R ) is false .
D. Assertion (A ) is false but reason (R ) is true.

Explanation

To solve the assertion and reason question, we will analyze both the assertion (A) and the reason (R) separately.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states: "Bt in Bt toxin represents Bacillus thuringiensis."
- Bacillus thuringiensis (Bt) is indeed a bacterium known for producing a protein that is toxic to certain insects. This protein is commonly referred to as Bt toxin. Therefore, the assertion is **true**.

2. **Understanding the Reason (R)**:
- The reason states: "Bt toxin is produced by a virus."
- This statement is incorrect. Bt toxin is produced by the bacterium Bacillus thuringiensis, not by a virus. Viruses do not produce Bt toxin. Therefore, the reason is **false**.

3. **Conclusion**:
- Since the assertion is true and the reason is false, we conclude that the correct answer is that the assertion is true, but the reason is false.

### Final Answer:
- Assertion (A) is true, and Reason (R) is false.