Question

For $Zn^{2+}$, $Ni^{2+}$, $Cu^{2+}$ and $Cr^{2+}$ which of the following statements is correct?

• A. Only $Zn^{2+}$ is colourless and $Ni^{2+}$, $Cu^{2+}$ and $Cr^{2+}$ are coloured
• B. All the ions are coloured
• C. All the ions are colourless
• D. $Zn^{2+}$ and $Cu^{2+}$ are colourless while $Ni^{2+}$ and $Cr^{2+}$ are coloured

Answer 1

Answer: (A)

$Zn^{2+}(3d^{10})$ has zero unpaired electron (colourless).
$Ni^{2+}(3d^8)$ has $2$ unpaired electrons (coloured).
$Cu^{2+}(3d^9)$ has $1$ unpaired electron (coloured).
$Cr^{2+}(3d^4)$ has $4$ unpaired electrons (coloured).