Menadione (Vitamin $\mathbf{K}_3$)

Correct Answer: A

Rationale: Menadione can cause hemolysis in G6PD deficiency due to oxidative stress; it’s not preferred for other uses listed.

Correct Answer: C

Rationale: Folinic acid (leucovorin) rescues cells from methotrexate toxicity by bypassing folate inhibition.

Correct Answer: A

Rationale: Penicillamine is an oral chelator effective in lead poisoning; it’s unrelated to penicillin structurally, so no cross-allergy occurs.

Correct Answer: B

Rationale: Succimer (DMSA) is less toxic than dimercaprol, effective orally, and safe in children for lead chelation.