Chemistry - Coordination Chemistry Question with Solution | TestHub

(A) is NOT correct: unpaired electrons are ${\mathrm{V}}^{2+}{\mathrm{d}}^3(3),{\mathrm{Cr}}^{2+}{\mathrm{d}}^4(4),{\mathrm{Mn}}^{2+}{\mathrm{d}}^5(5),{\mathrm{Fe}}^{2+}{\mathrm{d}}^6(4)$, so the paramagnetic moment order is ${\mathrm{V}}^{2+}<{\mathrm{Cr}}^{2+}={\mathrm{Fe}}^{2+}<{\mathrm{Mn}}^{2+}$ - the given order ends with ${\mathrm{Mn}}^{2+}<{\mathrm{Fe}}^{2+}$, which is wrong.

(B) correct: ionic size decreases across the series, ${\mathrm{Mn}}^{2+}>{\mathrm{Fe}}^{2+}>{\mathrm{Co}}^{2+}>{\mathrm{Ni}}^{2+}$.

(C) correct: in water ${\mathrm{Co}}^{3+}$ is strongly oxidising (least stable) while ${\mathrm{Sc}}^{3+}$ is most stable, so ${\mathrm{Co}}^{3+}<{\mathrm{Fe}}^{3+}<{\mathrm{Cr}}^{3+}<{\mathrm{Sc}}^{3+}$.

(D) correct: the number of accessible oxidation states increases $\mathrm{Sc}<\mathrm{Ti}<\mathrm{Cr}<\mathrm{Mn}$.

Answer: (A)