$(II)$ Tetrahedral $Ni(II)$ complex can very rarely be low spin because square planar (under strong ligand) complexes of $Ni ( II )$ are low spin complexes.

$(III)$ With strong field ligands $Mn (II)$ complexes can be low spin because they have less number of unpaired electron (unpaired electron $=1$ )

While with weak field ligands $Mn(II)$ complexes can be high spin because they have more number of unpaired electron (unpaired electron $=5)$

$(IV)$ Aqueous solution of $Mn(II)$ ions is pink in colour.