Which of the following compounds is diamagnetic and tetrahedral?

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 $:$

Match the List-$I$ with List-$II$

List-$I$ (Molecules/ion)	List-$II$ (Hybridisation of central atom)
$A. PF_5$	$I. dsp^2$
$B. SF_6$	$II. sp^3d$
$C. Ni(CO)_4$	$III. sp^3d^2$
$D. [PtCl_4]^{2-}$	$IV. sp^3$

Choose the correct answer from the options given below $:$

The hybridisation and geometry of $[Ni(CN)_4]^{2-}$ are:

Geometrical shapes of the complexes formed by the reaction of $Ni^{2+}$ with $Cl^{-}$,$CN^{-}$,and $H_2O$,respectively,are

An aqueous solution of $NiCl_{2}$ was heated with excess sodium cyanide in the presence of a strong oxidizing agent to form $[Ni(CN)_{6}]^{2-}$. The total change in the number of unpaired electrons on the metal centre is $.....$