Which of the following complex is/are homoleptic?

a. Co(NH3)63+
b. Co(NH3)5Cl2+
c. Ni(CN)42-
d. Ni(NH3)4Cl2

Choose the correct option
1. (a, b)
2. (b, c)
3. (c, d)
4. (a, c)

Homoleptic complex The complex containing only one species or group as ligand is known as homoleptic ligand.

e.g., Co(NH3)63+, Ni(CN)42-

Here, Co(NH3)63+ contain only NH3 as a ligand and Ni(CN)42- contains CN as a ligand.

While the other two complexes Co(NH3)5Cl2+ and Ni(NH3)4Cl2 contain and Cl as ligands. 

Hence, options (a) and (c) are correct choiece.