For the disproportionation of copper 2Cu+------ Cu2+ + Cu, E(standard)cell is (given E for Cu2+/Cu is 0.34V and E for Cu2+/Cu+ is 0.15V)
1- 0.49V 2- -0.19V
3- 0.38V 4- -0.38V
2Cu+ ..................... Cu2+ + Cu Eocell= ?
Cu2+ + 2e ..................... Cu ECu2+/Cu= 0.34V
Cu2+ + e ..................... Cu+ ECu2+/Cu+= 0.15V
Cu+ + e .................... Cu ECu+/Cu = 0.53V
So, EoCu+/Cu2+= 0.53-0.15 = 0.38V
Cu2+ + 2e ..................... Cu ECu2+/Cu= 0.34V
Cu2+ + e ..................... Cu+ ECu2+/Cu+= 0.15V
Cu+ + e .................... Cu ECu+/Cu = 0.53V
So, EoCu+/Cu2+= 0.53-0.15 = 0.38V