Question

Which of the following cannot be a ligand?

(a) Ni^2+

(b) Cl^–

(c) H2O

(d) NH3

I got this question in a national level competition.

My doubt stems from Definitions in section Coordination Compounds of Chemistry – Class 12

Answer 1

The correct choice is (a) Ni^2+

The explanation is: The ions/molecules bound to the central atom/ion is called a ligand. Ni^2+ is a metal ion, and according to Werner the secondary valences can be satisfied only by neutral molecules or negative ions. Cl^–, H2O and NH3 are all possible ligands.