What is the coordination number of \( Ni \) in \( [Ni(NH_3)_4]^{2+} \) complex?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 4
The coordination number of a metal ion in a complex is the number of ligand donor atoms directly bonded to it. For unidentate ligands it equals the number of ligands; a didentate ligand counts twice.
In \( \ce{[Ni(NH3)4]^2+} \), each \( \ce{NH3} \) is a unidentate ligand that binds through the lone pair on its nitrogen atom. Four \( \ce{NH3} \) molecules give four Ni–N bonds:
\( \displaystyle \text{CN} = 4 \times 1 = 4 \)
So the coordination number of Ni is 4. The hydrogen atoms of \( \ce{NH3} \) are not bonded to the metal and are not counted.
NCERT (2026-27 edition):
Coordination Number
