A body is heated by giving amount of heat energy ? Will its mass increase or decrease or remain constant ? If it increases or decreases, then by how much?

The variation in mass depends on the nature of body. For most solids, there is no variation in mass On heating. However, if the solid is volatile, heating will change the mass of the solid. Heating of solids in general bring about a change in state and during this process some loss of mass occurs due to evaporation.