Q. Why Zinc loses electron more easily than Copper?
Because Zn has more oxidation potential than Cu. Simply Zn is more Electropsitive than Cu. (Zn, E°(red): -0.76V. Cu, E°(red): +0.34V). Secondly zinc has greater covalent and ionic radii values than copper. (Covalent radius of zinc is 125pm and its ionic radius is 88pm while the covalent radius of copper is 117pm while its ionic radius is 87pm). The inner d-orbitals of zinc are fully filled thus offer more shielding effect and so there is slight increase in size.
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