Largest known virus is

Options

A. TMV
B. `T_(1)` phage
C. Citrus tristeza
D. `phi xx 174`

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the largest known virus among the given options: TMV (Tobacco Mosaic Virus), T1 phage, Citrus Tristeza Virus (CTV), and Psi 174.

2. **Analyzing Each Option**:
- **TMV (Tobacco Mosaic Virus)**:
- Type: Positive sense single-stranded RNA virus.
- Size: Approximately 300 nanometers in length and 18 nanometers in diameter.
- Genome Size: 6.3 to 6.5 kilobase pairs.
- **T1 Phage**:
- Type: Bacteriophage (virus that infects bacteria).
- Size: Much smaller than typical viruses.
- Genome Size: Approximately 50,000 base pairs (double-stranded DNA).
- **Citrus Tristeza Virus (CTV)**:
- Type: Positive sense single-stranded RNA virus.
- Size: Approximately 2000 nanometers in length and 12 nanometers in diameter.
- Genome Size: 19.3 kilobase pairs.
- **Psi 174**:
- Type: Positive sense single-stranded DNA virus.
- Size: Much smaller than CTV.
- Genome Size: Approximately 5386 nucleotides.

3. **Comparing Sizes**:
- Among the options, CTV is the largest with a length of 2000 nanometers, while TMV is significantly smaller at 300 nanometers. T1 phage and Psi 174 are even smaller.

4. **Conclusion**: Based on the analysis, the largest known virus from the provided options is **Citrus Tristeza Virus (CTV)**.

### Final Answer:
The largest known virus is **Citrus Tristeza Virus (CTV)**.

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