Question

Following are the transition metal ions of 3d series:

Ti⁴⁺, V²⁺, Mn³⁺, Cr³⁺

(Atomic numbers: Ti = 22, V = 23, Mn = 25, Cr = 24)

Answer the following:

1) Which ion is most stable in an aqueous solution and why?

2) Which ion is a strong oxidising agent and why?

3) Which ion is colourless and why?

Answer 1

1)

Gaseous ions	Number of unpaired electrons
Ti4+, [Ar] 3d0	0
V2+, [Ar] 3d3	3
Mn3+, [Ar] 3d4	4
Cr3+, [Ar] 3d3	3

V²⁺ and Cr³⁺ are the most stable ions in aqueous solutions owing to ${\displaystyle t_{2g}^3}$ a configuration.

2) An examination of the Eo values for the redox couple M³⁺/M²⁺ (from electrode potential table) shows that Mn³⁺ ion are the strongest oxidising agents in aqueous solutions.

3) Only the ions that have electrons in d-orbital and in which d-d transition is possible will be coloured. The ions in which d-orbitals are empty or completely filled will be colourless as no d-d transition is possible in those configurations.
From the given transition metal ions, it can be easily observed that only Ti⁴⁺ has an empty d-orbital, so, it is colourless ion.