How would you account for the following :
The `d^(1)` configuration is very unstable in ions.

Explanation

Transition metal ions with `d^(1)` configuration have the tendency to lose the only electron present in (n - 1) d subshell to produce an ion with stable `d^(0)` configuration (having noble gas electronic structure). Thus, ions with `d^(1)` configuration are not stable and usually undergo oxidation or disproportionation.