Question

Of the ions $Z{n}^{2+},N{i}^{2+}adC{r}^{3+}$ (atomic number of and Cr = 24)

• A. all these are colourless
• B. all these are coloured
• C. only $N{i}^{2+}$ is coloured and $Z{n}^{2+}$ and $C{r}^{3+}$ are colourless
• D. only $Z{n}^{2+}$ is colourless and $N{i}^{2+}$ and $C{r}^{3+}$ are coloured

Answer 1

Answer: (D)

The ions having unpaired electrons are coloured.
$Z{n}^{2+}=1s^2,2s^2,2p^6,3s^2,3p^6,4s^o,3d^{10}$
$C{r}^{3+}=1s^2,2s^2,2p^6,3s^2,3p^6,4s^0,3d^3$
$N{i}^{2+}=1s^2,2s^2,2p^6,3s^2,3p^6,4s^0,3d^8$
$\therefore$ Only $Z{n}^{2+}$ is colourless as it has all electrons paired.
$\therefore C{r}^{3+}$ and $N{i}^{2+}$ are coloured due to the presence of unpaired electrons.