(a) Following are the transition metal ions of 3d series :
`Ti^(4+),V^(2+),Mn^(3+),Cr^(3+)`
(Atomic numbers : Ti = 22, V = 23, Mn = 25, Cr = 24)
Answer the following :
(i) Which ion is most stable in an aqueous solution and why ?
(ii) Which ion is a strong oxidising agent and why ?
(iii) Which ion is colourless and why ?
(b) Complete the following equations :
(i) `2MnO_(4)^(-)+16H^(+)+5S^(2-)to`
(ii) `KMnO_(4)overset("Heat")to`

Explanation

(a) (i) `Cr^(3+)` ion is most stable in an aqueous solution because it has stable half-filled `(t_(2g))` configuration.
(ii) `Mn^(3+)` is a strong oxidising agent because `Mn^(2+)` formed as a result of reduction has half-filled `(d^(5))` stable configuration.
(iii) `Ti^(4+)` is colourless. There is no possibility of d-d transition and hence no absorption of light.
(b) (i) `2MnO_(4)^(-)+16H^(+)+5S^(2-)to2Mn^(2+)+8H_(2)O+5S`
(ii) `2KMnO_(4)overset("Heat")toK_(2)MnO_(4)+MnO_(2)+O_(2)`