The IR stretching frequencies of free $\mathrm{CO}$, and $\mathrm{CO}$ in ${[\mathrm{V}{\left(\mathrm{CO}\right)}_6 ]}^{-}, [\mathrm{Cr}{\left(\mathrm{CO}\right)}_6{]}^0$ and ${\left[\mathrm{Mn}(\mathrm{CO}{)}_6\right]}^{+}$ are $2143 {\mathrm{cm}}^{-1}$, $1860 {\mathrm{cm}}^{-1}$, $2000 {\mathrm{cm}}^{-1}$and $2090 {\mathrm{cm}}^{-1}$, respectively. The correct statement about metal carbonyls is :

$\text{'}\mathrm{M}-\mathrm{C}\text{'}$ pi bonding is higher in the cation.

$\text{'}\mathrm{C}-\mathrm{O}\text{'}$bond is weakest in the cation and strongest in the anion

$\text{'}\mathrm{C}-\mathrm{O}\text{'}$ bond is strongest in the cation and weakest in the anion.

$\text{'}\mathrm{C}-\mathrm{O}\text{'}$ bond is longer in the cation than in the anion.