2003 AIPMT The d- and f-Block ElementsOxides of Transition Metals Medium Question 70 of 76 in The d- and f-Block Elements

The basic character of the transition metal monoxides follows the order : (Atomic nos. Ti = 22, V = 23, Cr = 24, Fe = 26)

A VO > CrO > TiO > FeO
B CrO > VO > FeO > TiO
C TiO > FeO > VO > CrO
D TiO > VO > CrO > FeO

The answer is D.

Solution

In all these monoxides the metal is in the +2 oxidation state.
Across the 3d series (Ti to Fe), the nuclear charge increases and the ionic radius of $M^{2+}$ decreases. This increases the covalent character of the M–O bond and makes the oxide less ionic, and so less basic.
So the basic character decreases as the atomic number increases: Ti (22) $\gt$ V (23) $\gt$ Cr (24) $\gt$ Fe (26).
The order is TiO $\gt$ VO $\gt$ CrO $\gt$ FeO.

Concept Basicity of oxides across 3d series

The d- and f-Block Elements in past papers

76 questions from this chapter have appeared across 27 exam years.