This is a redox reaction, meaning reduction-oxidation reaction. This represents the reaction in one side of the electrode in an electrolysis set-up. First, we find the oxidation number of Cu in CuSO4:
(ox. # of Cu)+ ox.# of S + 4(ox.# of oxygen) = 0
(ox. # of Cu) + (6) + 4(-2) = 0
ox. # of Cu = 2+
CuSO4 ---> Cu + SO42-
Cu2+ + SO42- ----> Cu + SO42-
Cu2+ -----> Cu + 2e- (net ionic reaction)
The stoichiometric equation would be 2 electrons per mole Copper. Copper has a molar mass of 63.5 g/mol. Then, it would only need 2 electrons.