Question

What is the charge on a monodentate ligand X in the complex, [NiX₄]^2-?

Answer 1

The charge number of the complex ion is – 2. 

Nickel being divalent, its oxidation state is + 2.

If the charge on monodentate ligand X is y, then 

Charge number = charge on Ni²⁺ charge on 6X – 2 = + 2 + 4 xy

∴ y = – 1

Hence the charge on ligand X is – 1.