Question:
The lanthanide ion that would show colour is :
Correct Option: , 2
Solution:
$\mathrm{Sm}=4 f^{6} 6 s^{2}$
$\mathrm{Sm}^{3+}=4 f^{5}=$ Partially filled $f$ orbital
$\therefore \mathrm{Sm}^{3+}$ will be coloured
$\mathrm{Lu}^{3+}=4 f^{14}=$ colourless.