**Core Concept**
Palivizumab is a monoclonal antibody used for the prophylaxis of respiratory syncytial virus (RSV) infection in high-risk infants. RSV is a common viral infection that affects the respiratory system, particularly in young children.

**Why the Correct Answer is Right**
Palivizumab targets the RSV fusion protein, which is essential for the virus's entry into host cells. By binding to this protein, palivizumab prevents viral replication and subsequent infection. Palivizumab is administered intramuscularly on a monthly basis during the RSV season to provide protection against severe RSV disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Rituximab is a monoclonal antibody used in the treatment of non-Hodgkin's lymphoma and autoimmune diseases, but it is not used for RSV infection. Rituximab targets the CD20 antigen on B cells, which is unrelated to RSV.
**Option C:** Penicillin is an antibiotic used to treat bacterial infections, and it has no role in the treatment or prevention of RSV infection. RSV is a viral infection, and antibiotics are ineffective against viral pathogens.
**Option D:** This option is incorrect because there is a specific drug used for the prevention of RSV infection, which is palivizumab.

**Clinical Pearl / High-Yield Fact**
Palivizumab is most effective in preventing severe RSV disease in high-risk infants, such as those with pre-existing respiratory conditions or congenital heart disease. Regular administration of palivizumab during the RSV season can significantly reduce the risk of hospitalization due to RSV infection.

**✓ Correct Answer: B. Palivizumab**