The complex cation which has two isomers is:
\( \text{[Co(NH}_3\text{)}_5\text{Cl]}^{2+} \)
\( \text{[Co(H}_2\text{O)}_6]^{3+} \)
\( \text{[Co(NH}_3\text{)}_5\text{Cl]}^{+} \)
\( \text{[Co(NH}_3\text{)}_5\text{NO}_2]^{2+} \)