d- and f-Block Elements · Question 41

The amphoteric oxide among V2O3, V2O4 and V2O5, upon reaction with alkali leads to formation of an oxide anion. The oxidation state of V in the oxide anion is :

1. + 4
2. + 5
3. + 3
4. + 7

Answer

(2) + 5

Solution

Acidic character of oxides of a transition metal increases with oxidation state: V2O3 (+3) is basic, V2O4 (+4) is less basic, and V2O5 (+5) is amphoteric, though mainly acidic (NCERT).

With alkali, V2O5 gives vanadate ions:

V2O5 + 6OH- 2VO43- + 3H2O

In VO43-: x + 4(-2) = -3 x = +5

(the oxidation state does not change in this acid–base reaction).

Answer: (2)