In the following ions :
`Mn^(3+),V^(3+),Cr^(3+),Ti^(4+)`
(Atomic no. : Mn = 25, V = 23, Cr = 24, Ti = 22)
(a) Which ion is most stable in an aqueous solution ?
(b) Which ion is the strongest oxidising agent ?
(c) Which ion is colourless ?
(d) Which ion has the highest number of unpaired electrons ?

Explanation

`Mn^(3+),V^(3+),Cr^(3+),Ti^(4+)`
(a) `Cr^(3+)` has the highest negative electrode potential, therefore, it is most stable.
(b) `Mn^(3+)` has `d^(4)` configuration, it has the maximum tendency to gain one electron to change into stable half filled configuration, `d.^(5)`. Therefore it is the strongest oxidising agent.
(c) `Ti^(4+)` has no electrons in the d-orbital, therefore no absorption of light and hence colourless.
(d) `Mn^(3+)` has `d^(4)` configuration. The electrons occupy different orbitals. It has the highest number of unpaired electrons among the four.