Question

In $\left[Co\right(CN{)}_6{]}^{4-}$ and $\left[Co\right(CN{)}_6{]}^{3-}$:

• A. one is paramagnetic
• B. second is diamagnetic
• C. one is diamagnetic and second is paramagnetic
• D. both A and B

Answer 1

The correct option is D both A and B

We know that,
$C{o}^{+2}$ ion is present in $\left[Co\right(CN{)}_6{]}^{-4}$ while $C{o}^{+3}$ ion is present in $\left[Co\right(CN{)}_6{]}^{-3}$.
The attached image shows the Electronic Configuration of $C{o}^{+2}$ and $C{o}^{+3}$ ions in the ground state.
While in the excited state, and undergoing hybridisation, $C{N}^{-}$ being a strong field ligand forces the inner d electrons to pair up.
Due to this, $C{o}^{+2}$ in $\left[Co\right(CN{)}_6{]}^{-4}$ has one unpaired electron(i.e. it is paramagnetic) whereas, $C{o}^{+3}$ in $\left[Co\right(CN{)}_6{]}^{-3}$ has no unpaired electron(i.e. it is diamagnetic).
Hence the given statement is True. So we write $1$.