Give examples and suggest reasons for the following features of the transition metals.
The lowest oxide of transition metal is basic, the highest is amphoteric/acidic.

Explanation

(a) The lower oxide of transition metal having low oxidation state is basic whereas the higher oxide of transition metal having high oxidation state is amphoteric or acidic. For example, MnO (II) is basic while `Mn_2O_7` (VII) is acidic. Similarly, CrO (II) is basic while `Cr_2O_3` (III) is amphoteric.
(b) A transition metal exhibits higher oxidation states in oxides and fluorides because oxygen and fluorine are of small size and high electronegativity and hence can readily oxidise the metals. For example, `OsF.[Os(VI)], V_2O_5[V(V)]` .
( c) Oxoanions of metals have highest oxidation states. For example, Cr in `Cr_2O_7^(2-)` has an oxidation state of +6 whereas Mn in `MnO_4^(-)` has an oxidation state of +7. This is because of high electronegativity of oxygen and is high oxidising property.