A single stranded DNA is present in-

Options

A. TMV
B. Salmonella
C. Coliphage `phi xx 174`
D. Bacteria

Answer

To determine where single-stranded DNA is present, we can analyze the options provided:

1. **Tobacco Mosaic Virus (TMV)**: This virus contains RNA, not DNA. Therefore, it does not have single-stranded DNA.

2. **Salmonella**: This is a type of bacteria that typically contains double-stranded DNA. Thus, it does not fit the criteria for single-stranded DNA.

3. **Coliphage φX174**: This is a bacteriophage, which is a virus that infects bacteria. It is known to have a circular single-stranded DNA genome. This makes it a candidate for the presence of single-stranded DNA.

4. **Bacteria**: Generally, bacteria have double-stranded DNA, so they do not have single-stranded DNA.

Based on this analysis, the only option that contains single-stranded DNA is:

**Answer: Coliphage φX174 (Option 3)**

### Step-by-Step Solution:
1. **Identify the Options**: Look at the organisms provided in the question.
2. **Analyze Each Option**:
- **Tobacco Mosaic Virus**: Contains RNA, not DNA.
- **Salmonella**: Contains double-stranded DNA.
- **Coliphage φX174**: Contains circular single-stranded DNA.
- **Bacteria**: Typically have double-stranded DNA.
3. **Determine the Correct Answer**: The only option with single-stranded DNA is Coliphage φX174.