On a cold day when a room temperature is 15oC, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15oC, because A. metals have higher thermal capacity than plastics B. plastics have a lower density than metals C. metals are good conductor of heat D. plastics have a higher thermal conductivity than metals

The correct answer is C. metals are good conductor of heat.

Metals are good conductors of heat because they have free electrons that can move easily. These free electrons can carry heat energy from one part of the metal to another. This is why metals feel cold to the touch when they are in contact with a colder object.

Plastics, on the other hand, are not good conductors of heat. This is because plastics do not have free electrons. The heat energy in a plastic object is transferred by the movement of molecules. This is a much slower process than the transfer of heat energy in a metal object.

Therefore, the metallic cap of a pen becomes much colder than its plastic body on a cold day when the room temperature is 15oC because metals are good conductors of heat.