What is the trend of M+3/M+2 standard electrode potential for transition metals?

Dear Student,
The standard electrode potential is actually reduction potential. The loss in electrons is reduction. We need to look at the electronic configuration of various M3+ cations of transition series in order to see the trend. The half fillled and fully filled configurations are more stable, so losing an electron from them in order to become M2+ cation would be difficult. Therefore such ions would consitute low E values.