Dear Student,
Copper has high enthalpy of atomisation whereas Zinc has least enthalpy of atomisation due to the absence of any unpaired electron in Zn. Cu however contains an unpaired electron in the 4s orbital.
Enthalpy of atomisation depends on the metallic bonding and higher the number of unpaired electrons, higher will be the metal-metal bond.
Hence, Zn has least enthalpy of atomisation whereas Cu has high enthalpy of atomisation.