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 colured
• C. All the ions are colourless
• D. $Zn^{2 +}$ and $Cu^{2 +}$ are colourless while $Ni^{2 +}$ and $Cr^{2 +}$ are colured.

Answer 1

Answer: (A)

Only $Zn^{2 +}$is colourless and $Ni^{2 +},Cu^{2 +}$ and $Cr^{2 +}$ are coloured.

Answer 2

$Zn^{2 +}(3d)^{10}$ 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)