'X' is the mode of transmission of heat that takes place by the movement of hot particles. Identify 'X'.
Convection
Convection is the mode of transfer of heat by the bulk movement of particles in fluids such as gases and liquids. Conduction takes place in solids where heat transfer takes place through the vibration of molecules. Radiation doesn't require a medium for heat transfer. For example, the transfer of heat from the sun to the earth.