The magnetic moment of an octahedral homoleptic $\mathrm{Mn}\left(\mathrm{II}\right)$ complex is $5.9\mathrm{B}.\mathrm{M}.$ . The suitable ligand for this complex is:

$M{n}^{2+}$ will have configuration $=3d^{5}4s^0$

$\mu =5.93=\sqrt{n\left(n+2\right)}$

or, $n=5$ as $\sqrt{35}=5.93$

If has $5$ unpaired electron which are not getting paired up. This implies that the ligand paired up, and the ligand is a weak field ligand. Among the given options, weak ligand is $NC{S}^{-}$