The aqueous solutions of the following salts will be coloured in the case of\

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Professor PC Thomas Classes · Answer

(c,d): $\mathrm{Co}^{2+}$ [in aqueous solution of $\mathrm{Co}\left(\mathrm{NO}_{3}ight)_{2}$ ] and $\mathrm{Cr}^{3+}\left(ight.$ in $\left.\mathrm{CrCl}_{3}ight)$ have the outer configuration as $d^{7}$ and $d^{3}$ respectively. Since both $\mathrm{Co}^{2+}$ and $\mathrm{Cr}^{3+}$ have incompletely filled $d$-orbitals so the aqueous solutions of $\mathrm{Co}\left(\mathrm{NO}_{3}ight)_{2}$ and $\mathrm{CrCl}_{3}$ are coloured ( $d-d$ transitions are possible).\