Which portable fire extinguisher is required just outside the exit of the propulsion machinery space of a 75-ton passenger vessel?

Correct Answer: Option B — 15 lb. CO2 extinguisher

46 CFR Subchapter T requires a 15 lb. CO2 extinguisher or equivalent located just outside the propulsion machinery space exit. This placement allows crew members to access the extinguisher quickly to combat engine room fires without entering the hazard zone, ensuring safety during fire suppression efforts.