Which of the following oxides is amphoteric in nature ?

Options

A. `Mn_(2)O_(7)`
B. `MnO_(2)`
C. `Cr_(2)O_(3)`
D. both (2) and (3)

Answer

D

Explanation

The acidic/basic character of transition metal oxide changes with the oxidation state. Low oxidation states are more basis and more ionic while high oxidation states are more acidic and more covalent. MnO and `Mn_(2)O_(3)` are basic oxides as `Mn^(4+)` ions. `Mn(+5)` is rather uncommon. `Mn(+6)` is represented by manganates such as `Na_(2)MnO_(4)`. This may be regarded as a salt of the unstable acidic oxide `MnO_(3)`. which does not exist in the free state. `Mn(+7)` occurs as `Mn_(2)O_(7)` which is strongly acidic. The corresponding acid, permanganic acid `HMnO_(4)`, is a very strong acid. `MnO_(2)` is used in ,dry batteries' (Leclanche cells). For this purpose it must be pure, and is made by electrolytic oxidation of `MnSO_(4)`. It is used in the brick indusrty to colour bricks red or brown. It is used to make red or purple glass. The oxide `Cr_(2)O_(3)` becomes inert to acids and bases if heatred strongly but otherwies it is amphoteric, giving `[Cr(H_(2)O)_(6)]^(3+)` with acids, and chromites with concentrated alkali.