Standard electrode potentialEM+2/M0 of a d- block element depends on various factors. EM+2/Mo  is positive when ‘M’ is

The exothermic hydration enthalpy is not sufficient to compensate the sum of endothermic nature  of     ΔHatomization,       ΔHIE1+IE2;∴   Cus→   Cu+2aq  is most difficult.; ECu+2/Cu0 is positive;