**Core Concept**
The capsule of pneumococcus is a critical virulence factor composed of a specific type of carbohydrate molecule that surrounds the bacterial cell, providing protection from phagocytosis and contributing to the development of invasive pneumococcal disease.

**Why the Correct Answer is Right**
The capsule of pneumococcus is primarily composed of polysaccharides, which are long chains of sugar molecules. These polysaccharides are produced by the bacterial cell and are responsible for the virulence of pneumococcus. The capsule helps to evade the host's immune system by preventing the activation of complement and inhibiting phagocytosis. The specific type of polysaccharide present in the capsule determines the serotype of pneumococcus, with over 90 distinct serotypes identified. The capsule plays a crucial role in the pathogenesis of pneumococcal infections, including pneumonia, meningitis, and sepsis.

**Why Each Wrong Option is Incorrect**
**Option A:** Polypeptide - While pneumococcus does produce polypeptides, the capsule is not composed of polypeptides.
**Option C:** Lipopolysaccharide - Lipopolysaccharides are characteristic of gram-negative bacteria, such as E. coli, and are not components of pneumococcus capsules.
**Option D:** Not a Virulence factor - The capsule is a critical virulence factor for pneumococcus, and its absence or modification leads to reduced virulence.

**Clinical Pearl / High-Yield Fact**
Pneumococcal conjugate vaccines, such as Prevnar, target specific serotypes of pneumococcus and have been shown to be highly effective in preventing invasive pneumococcal disease in children and adults. Understanding the role of the capsule in pneumococcal virulence is essential for developing effective vaccine strategies.

✓ Correct Answer: B. Polysaccharide.