S. strain of Diplococcus is

Options

A. Smooth, capsulated non virulent form causing death in mice
B. Smooth, non-capsulated virulent form causing no death in mice
C. Smooth, non-capsulated non virulent form causing no death in mice
D. Smooth, capsulated virulent form causing death in mice

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the characteristics of the S strain of Diplococcus, specifically its virulence and capsulation.

2. **Background Information**: The S strain of Diplococcus pneumoniae is known for its smooth appearance due to a polysaccharide capsule. This capsule plays a crucial role in its ability to evade the host's immune system.

3. **Identifying the Strains**:
- The S strain (smooth strain) is encapsulated and virulent, meaning it can cause disease and death in mice.
- The R strain (rough strain) lacks the capsule and is non-virulent, meaning it does not cause disease in mice.

4. **Analyzing the Options**:
- **Option A**: Smooth, capsulated, non-virulent form causing death in mice. (Incorrect: Non-virulent cannot cause death.)
- **Option B**: Smooth, non-capsulated, virulent form causing no death in mice. (Incorrect: Non-capsulated cannot be virulent.)
- **Option C**: Smooth, non-capsulated, non-virulent form causing no death in mice. (Incorrect: Smooth strain is capsulated.)
- **Option D**: Smooth, capsulated, virulent form causing death in mice. (Correct: This accurately describes the S strain.)

5. **Conclusion**: The correct answer is **Option D**: Smooth, capsulated, virulent form causing death in mice.