The $[\mathrm{Co}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{]}^{2+}$ion has three unpaired electrons. The hybridization of Co in $[\mathrm{Co}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{]}^{2+}$ is:

$\begin{array}{l}\mathrm{Co}\left(\mathrm{Z}=27\right)......\left[\mathrm{Ar}\right]4{\mathrm{s}}^{2}3{\mathrm{d}}^7\\ {\mathrm{Co}}^{+2}......\left[\mathrm{Ar}\right]3{\mathrm{d}}^7\end{array}$

Number of unpaired electrons = 3
Hybridization = ${\mathrm{sp}}^3{\mathrm{d}}^2$
Outer orbital complex