Which First row transition element exhibits stable +1 oxidation state

Explanation

Electronic configuration of `Cu=[Ar]3d^(10)4s^(1)`. When copper atom loses `1` electron, it exhibits `+1` oxidation state and forms `Cu^(+)` ion with stable `3d^(10)` configuration. So, copper metal in the first transition series tends to have `+1` oxidation state to achieve a stable configuration.