Assertion : Left-handed DNA is known as B-DNA.
Reason : Right - handed DNA is known as Z-DNA .

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion:** Left-handed DNA is known as B-DNA.
**Reason:** Right-handed DNA is known as Z-DNA.

### Step-by-Step Solution:

1. **Understanding DNA Types:**
- There are two common forms of DNA: B-DNA and Z-DNA.
- B-DNA is the most prevalent form of DNA in cells and is characterized by a right-handed helical structure.
- Z-DNA is a less common form that has a left-handed helical structure.

2. **Analyzing the Assertion:**
- The assertion states that left-handed DNA is known as B-DNA.
- This is incorrect because B-DNA is actually right-handed, not left-handed.

3. **Analyzing the Reason:**
- The reason states that right-handed DNA is known as Z-DNA.
- This is also incorrect because Z-DNA is left-handed, not right-handed.

4. **Conclusion:**
- Since both the assertion and the reason are false, the correct answer is that both A (Assertion) and R (Reason) are false.

### Final Answer:
Both the assertion and the reason are false.

---