The correct answer is (b) Mercury. Mercury is a metal that is liquid at room temperature. It is a very good conductor of heat and electricity. Water is also a good conductor of heat, but it is not as good as mercury. Benzene is a liquid hydrocarbon that is not a good conductor of heat. Leather is a material made from animal skin that is not a good conductor of heat.
Mercury is a good conductor of heat because it has free electrons that can move easily. These electrons can carry heat energy from one part of the mercury to another. Water is also a good conductor of heat because it has molecules that are constantly moving. These molecules can carry heat energy from one part of the water to another. Benzene is not a good conductor of heat because its molecules are not as good at moving as the molecules of water or mercury. Leather is not a good conductor of heat because it is made from animal skin, which is a poor conductor of heat.