The geometry of $[Ni(CO)_4]$ and $[NiCl_2(PPh_3)_2]$ are

Which one of the following ions is not tetrahedral in shape?

Nickel $(Z = 28)$ combines with a uninegative monodentate ligand $X^{-}$ to form a paramagnetic complex $[NiX_4]^{-2}.$ The number of unpaired electron$(s)$ in the nickel and geometry of this complex ion are,respectively $:$

In $[NiCl_4]^{2-}$,the number of unpaired electrons is

Which statement is incorrect regarding the complex $[HgI_3]^{-}$?

For octahedral $Mn(II)$ and tetrahedral $Ni(II)$ complexes,consider the following statements:
$(I)$ Both the complexes can be high spin.
$(II)$ $Ni(II)$ complex can very rarely be low spin.
$(III)$ With strong field ligands,$Mn(II)$ complexes can be low spin.
$(IV)$ Aqueous solution of $Mn(II)$ ions is yellow in color.