Question

For the ions $Z{n}^{2+},N{i}^{2+}$ and $C{r}^{3+}$ which among the following statements is correct?
(atomic number of $Zn=30,Ni=28$ 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 with unpaired electrons are coloured and those with paired electrons are colourless.
$\underset{\text{No. of }{e}^{-}s=28}{Z{n}^{2+}}=1s^2,2s^2{p}^6,3s^2{p}^6{d}^{10}$
$\underset{\text{No. of }{e}^{-}s=21}{C{r}^{3+}}=1s^2,2s^2{p}^6,3s^2{p}^6{d}^3$
$\underset{\text{ (No. of }{e}^{-}s=26)}{N{i}^{2+}}=1s^2,2s^2{p}^6,3s^2{p}^6{d}^8$
Thus $Z{n}^{2+},C{r}^{3+}$ and $N{i}^{2+}$ have zero, $3$ and $2$ unpaired electrons respectively.