The correct answer is D) one C-II hand portable fire extinguisher. According to the regulations for tank vessels on international voyages, the required number and type of hand portable fire extinguishers to be carried in the vicinity of the radio room exit is one C-II extinguisher. This is specified in the applicable fire safety regulations for tank vessels, which require a C-class extinguisher (for fires involving energized electrical equipment) of the larger C-II size to be located near the radio room exit. The other answer choices are incorrect because they do not meet the specific requirement for a C-II extinguisher. A B-I or B-II extinguisher would not be appropriate, as they are for class B fires (flammable liquids), not the necessary class C fire protection. Similarly, a smaller C-I extinguisher would not satisfy the regulatory requirement for the larger C-II size.