Name the oxometal anions of the first series of the transition metals in which the metal exhibits the oxidation state equal to its group number.

Explanation

(i) `MnO_(4)^(-)`: Manganese shows (+7) oxidation state which is equal to its group number 7.
(ii) `Cr_(2)O_(7)^(2-) and CrO_(4)^(2)`: In both these oxoanions, chromium is in (+6) oxidation state which is equal to its group number 6.
(iii) `VO_(2)^(+)`: Vanadium shows (+5) oxidation state which is equal to its group number 5.