`E^@` values for the half cell reactions are given below :
`Cu^(2+) + e^(-) to Cu^(+) , E^@`=0.15 V
`Cu^(2+) + 2e^(-) to Cu, E^@`=0.34 V
What will be the `E^@` of the half-cell : `Cu^(+) + e^(-) to Cu` ?