Question

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

• A. all these are colourless
• B. all these are coloured
• C. only $Ni ^{2+}$ is coloured and $Zn ^{2+}$ and $Cr ^{3+}$ are colourless
• D. only $Zn ^{2+}$ is colourless and $Ni ^{2+}$ and $Cr ^{3+}$ are coloured

Answer 1

Answer: (D)

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