**Core Concept**
Pneumococcus (Streptococcus pneumoniae) is a gram-positive bacterium that can be differentiated from other streptococci based on its unique characteristics, particularly its ability to produce a specific type of polysaccharide capsule and its susceptibility to certain antibiotics.

**Why the Correct Answer is Right**
The correct answer lies in the ability of pneumococcus to produce a polysaccharide capsule, specifically a capsular polysaccharide (CPS) that is composed of a specific type of sugar called teichoic acid. This capsule is a key virulence factor for pneumococcus, allowing it to evade the host's immune system and cause invasive disease. In contrast, other streptococci, such as Streptococcus pyogenes, do not produce a polysaccharide capsule and are therefore more easily phagocytosed by immune cells.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because pneumococcus can be differentiated from other streptococci based on its unique capsule, not its ability to produce alpha-hemolysis.
* **Option B:** This option is incorrect because pneumococcus is susceptible to optochin, a disinfectant that is commonly used to differentiate pneumococcus from other streptococci.
* **Option D:** This option is incorrect because pneumococcus can be differentiated from other streptococci based on its unique capsule, not its ability to produce a specific type of hemolysis.

**Clinical Pearl / High-Yield Fact**
Pneumococcus can be differentiated from other streptococci using a combination of biochemical tests, including optochin sensitivity and bile solubility. This is an important clinical distinction, as pneumococcus is a leading cause of invasive disease, including pneumonia, meningitis, and sepsis.

**Correct Answer:** B.