Identify the common ammonia complexes

For the given metal ions with ammonia as ligand, the usual complexes are:

• $Ni^{2+} \rightarrow [Ni(NH_3)_6]^{2+}$
• $Pt^{2+} \rightarrow [Pt(NH_3)_4]^{2+}$
• $Zn^{2+} \rightarrow [Zn(NH_3)_4]^{2+}$

Determine geometry of each complex

(i) $Ni^{2+}$ ammonia complex

• $Ni^{2+}$ has configuration: $[Ar]3d^8$
• With ammonia, nickel commonly forms the hexacoordinate complex $[Ni(NH_3)_6]^{2+}$.
• Coordination number $=6$, so geometry is octahedral.

(ii) $Pt^{2+}$ ammonia complex

• $Pt^{2+}$ is a $d^8$ metal ion of the $5d$ series.
• $5d^8$ metal ions like $Pt^{2+}$ strongly prefer square planar geometry for coordination number 4.
• Thus $[Pt(NH_3)_4]^{2+}$ is square planar.

(iii) $Zn^{2+}$ ammonia complex

• $Zn^{2+}$ has configuration: $[Ar]3d^{10}$
• It commonly forms $[Zn(NH_3)_4]^{2+}$.
• Four-coordinate $d^{10}$ zinc complexes are generally tetrahedral.

Thus, the geometries respectively are

$\text{octahedral, square planar, tetrahedral}$

Match with the options

• A: octahedral, square planar and tetrahedral ✅
• B: square planar, octahedral and tetrahedral ❌
• C: tetrahedral, square planar and octahedral ❌
• D: octahedral, tetrahedral and square planar ❌

Final answer

$\boxed{A}$