(i) The lower oxide of transition metal is basic because the metal atom has low oxidation state whereas highest is acidic due to highest oxidation state. For example , `overset(II) (MnO)` is basic whereas `overset(VII)(Mn_(2)O_(7))` is acidic (Refer in page) .
In the low oxidation state of metal, some of the valence electrons of the metal atom are not involved in bonding. Hence, it can donate electrons and behave as a base. In the higher oxidation state, valence electrons are involved in the bonding and are not available. Instead, effective nuclear charge is high. Hence, it can accept electrons and hence behave as acid.
(ii) A transition metal exhibits higher oxidation states in oxides and fluorides because oxygen and fluorine are highly electronegative elements, small in size ( and strongest oxidising agents). For example , osmium shows an oxidation states of `+6` in `OsF_(6)` and vanadium shows an oxidation state of `+5` in `V_(2)O_(5)`
(iii) Oxometal anions have highest oxidation state, e.g., Cr in `Cr_(2)O_(7)^(2-)` or `CrO_(4)^(2-)` has an oxidation state of `+6` whereas Mn in `MnO_(4)^(-)` has an oxidation state of `+7` . This is again due to the combination of the metal with oxygen , which electronegative and oxidizing element.
