(a) $Ni(CO)_4$, (b) $[Ni(CN_4)]^{2-}$ and (c) $[Pt(NH_3)_2Cl_2]$ are respectively ______ complexes.

(a) Tetrahedral, (b) square planar and (c) square planar

The correct answer is Option (4) → (a) Tetrahedral, (b) square planar and (c) square planar

Let’s identify the geometry of each complex:

(a) Ni(CO)₄

• Ni is in 0 oxidation state (d¹⁰).
• Forms sp³ hybridization → tetrahedral geometry.

(b) [Ni(CN)₄]²⁻

• Ni²⁺ is d⁸.
• CN⁻ is a strong field ligand → pairing of electrons.
• Forms dsp² hybridization → square planar geometry.

(c) [Pt(NH₃)₂Cl₂]

• Pt²⁺ is d⁸.
• Pt(II) complexes are characteristically square planar.