Which is wrong about nucleic acids ?

Options

A. DNA is single stranded in some viruses
B. RNA is double stranded occasionally
C. Length of one helix is 45 `Å` in B-DNA
D. One turn of Z-DNA has 12 bases

Explanation

To determine which statement about nucleic acids is incorrect, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "DNA is single-stranded in some viruses."
- This statement is incorrect. While some viruses do have single-stranded DNA, most DNA viruses are double-stranded. Therefore, this statement is wrong.

2. **Statement 2**: "RNA is double-stranded occasionally."
- This statement is also incorrect. RNA is typically single-stranded and does not form double-stranded structures under normal circumstances. While there are some exceptions in certain viruses, they are not the norm. Thus, this statement is wrong as well.

3. **Statement 3**: "The length of one helix is 45 angstrom in the B-DNA model."
- This statement is incorrect. The correct length of one complete turn of the B-DNA helix is 34 angstroms, not 45 angstroms. Therefore, this statement is also wrong.

4. **Statement 4**: "One turn of Z-DNA has 12 bases."
- This statement is correct. In the Z-DNA model, one complete turn indeed consists of 12 base pairs. Therefore, this statement is true.

### Conclusion:
The wrong statements about nucleic acids are:
- Statement 1: "DNA is single-stranded in some viruses."
- Statement 2: "RNA is double-stranded occasionally."
- Statement 3: "The length of one helix is 45 angstrom in the B-DNA model."

**The correct answer to the question is that all three statements (1, 2, and 3) are incorrect about nucleic acids.**