Which of the following complex is/are homoleptic?

a. ${\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{6}\right]}^{3+}$
b. ${\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{5}\mathrm{Cl}\right]}^{2+}$
c. ${\left[\mathrm{Ni}{\left(\mathrm{CN}\right)}_{4}\right]}^{2-}$
d. $\left[\mathrm{Ni}{\left({\mathrm{NH}}_{3}\right)}_{4}{\mathrm{Cl}}_{2}\right]$

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., ${\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{6}\right]}^{3+}$, ${\left[\mathrm{Ni}{\left(\mathrm{CN}\right)}_{4}\right]}^{2-}$

Here, ${\left[Co{\left(N{H}_{3}\right)}_{6}\right]}^{3+}$ contain only ${NH}_{3}$ as a ligand and ${\left[Ni{\left(CN\right)}_{4}\right]}^{2-}$ contains CN as a ligand.

While the other two complexes ${\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{5}\mathrm{Cl}\right]}^{2+}$ and $\left[\mathrm{Ni}{\left({\mathrm{NH}}_{3}\right)}_{4}{\mathrm{Cl}}_{2}\right]$ contain and Cl as ligands.

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