Q. Of the ions $Zn^{2 +},\ Ni^{2 +}$ and $Cr^{3 +}$, (atomic number of Zn=30, Ni=28, Cr=24)
A) All three are coloured
B) All three are colourless
C) Only $Zn^{2 +}$ is colourless and $Ni^{2 +}$ and $Cr^{3 +}$ are coloured
D) Only $Ni^{2 +}$ is coloured and $Zn^{2 +}$ and $Cr^{3 +}$ are colourless
Explanation
(c)
$Ni^{2 +}$ and $Cr^{2 +}$ are coloured due to presence of unpaired electrons. But $Zn^{2 +}$ is colourless because of absence of unpaired electrons
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.