Which statements are correct about the complex \({\text{[Cu(N}}{{\text{H}}_{\text{3}}}{{\text{)}}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}{\text{]}}\)?

I.     Oxidation state of copper is +2.

II.     Ammonia is a ligand.

III.     Chloride ions act as Lewis acids.

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

A

Although several teachers had concerns about this one, overall it was a fair question with half the students answering it correctly. Surprisingly a quarter of the students incorrectly identified chloride ions acting as Lewis acids.