Q.
Which group contains coloured ions out of
1. $Cu^{2+}$
2. $Ti^{4+}$
3. $Co^{2+}$
4. $Fe^{2+}$
The d-and f-Block Elements
Solution:
Colour of a compound is property of unpaired $d$-electrons.
Ion
$Cu^{2+}$
$Ti^{4+}$
$Co^{2+}$
$Fe^{2+}$
Electronic configuration
$3d^9$
$3d^0$
$3d^7$
$3d^6$
No. of unpaired electrons
1
0
3
4
Since $Cu^{2+}, Co^{2+}$ and $Fe^{2+}$ contain unpaired electrons these are coloured ions.
| Ion | $Cu^{2+}$ | $Ti^{4+}$ | $Co^{2+}$ | $Fe^{2+}$ |
| Electronic configuration | $3d^9$ | $3d^0$ | $3d^7$ | $3d^6$ |
| No. of unpaired electrons | 1 | 0 | 3 | 4 |