Question

In which of the following pairs are both the ions coloured in aqueous solution?
[At. No. : $Sc=21,Ti=22,Ni=28,Cu=29,Co=27$]

• A. $N{i}^{2+},T{i}^{3+}$
• B. $S{c}^{3+},T{i}^{3+}$
• C. $S{c}^{3+},C{o}^{2+}$
• D. $N{i}^{2+},C{u}^{+}$

Answer 1

The correct option is A $N{i}^{2+},T{i}^{3+}$

$\left(I\right)$ $Ni\left[Ar\right]3d^{8}4s^2$

$N{i}^{+2}\left[Ar\right]3d^8$

$2$ unpaired $e^{-}s⟶$ paramagnetic.

$\left(II\right)$ $Cu\left[Ar\right]3d^{10}4s^1$

$C{u}^{+}\left[Ar\right]3d^{1}0$

$0$ unpaired $e^{-}s⟶$ dimagnetic.

$\left(III\right)$ $Ti\left[Ar\right]3d^{2}4s^2$

$T{i}^{+3}\left[Ar\right]3d^1$

$1$ unpaired $e^{-}s⟶$ paramagnetic.

$\left(IV\right)$ $Sc\left[Ar\right]3d^{1}4s^2$

$S{c}^{+3}\left[Ar\right]$

$0$ unpaired $e^{-}s⟶$ dimagnetic.

$\left(V\right)$ $Co\left[Ar\right]3d^{7}4s^2$

$C{o}^{+2}\left[Ar\right]3d^7$

$3$ unpaired $e^{-}s⟶$ paramagnetic.

Ions which are paramagnetic show colour in aqueous solution.