Considering H_2 O as weak field ligand, the number of unpaired...

Mn in $\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} is present as$\mathrm{Mn}^{2+}\left(3 d^5\right)$. <img src="https://cdn-question-pool.Quantrex.app/pyq/jipmer/of2KFryMPP9GItJY1MaBOqlYIvZNhVxvyrLiGq18l5A.original.fullsize.png"/>$s p^3 d^2$hybridisation occurs in \left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$. Due to the presence of weak field ligand pairing of electron does not take place, hence the number of unpaired electrons is five.