When two ends of a metal rod is kept at different temperatures, heat is conducted from hot end to cold end due to 

detailed solution

Correct option is C

During conduction of heat energy of vibration of atoms is transferred from one layer of atoms to the adjacent layer. Also as temperature increases, kinetic energy of free electrons increases like increase in kinetic energy of gas molecules. When these highly energitic electrons diffuse to colder regions, they collide with ionic cores and transfer their additional energy to the ionic cores thereby increasing the energy of vibration of the ionic cores.