Question

Which ion is colourless:

• A. $Cr^{+4}$
• B. $Sc^{+3}$
• C. $Ti^{+3}$
• D. $V^{+3}$

Answer 1

Answer: (B)

$Sc^{+3}$

Answer 2

Scandium ion $(Sc^{+3})$ is colorless. Scandium is a transition metal, and when it loses three electrons to form the $Sc^{+3}$ ion, it does not have any unpaired electrons in its d-orbital. This absence of unpaired electrons means that it does not absorb visible light, which is why it appears colorless.

So, the correct option is (B): $Sc^{+3}$