1 \(\left[\mathrm{Cr}(\text { en })_{3}\right] \mathrm{Br}_{2}\)
2 \(\left[\mathrm{Cr}(\mathrm{en})_{2} \mathrm{Br}_{2}\right] \mathrm{Br}\)
3 \(\left[\mathrm{Cr}(\mathrm{en}) \mathrm{Br}_{4}\right]^{-}\)
4 \(\left[ {{\rm{Cr(}}} \right.{\rm{en}}\left. {{\rm{)B}}{{\rm{r}}_{\rm{2}}}} \right]{\rm{Br}}\)
Explanation:
Two \(\mathrm{Br}\), two (en) and one \(\mathrm{Cr}\) are parts of complex.
Charge on the complex is
\[\left. \begin{gathered}
{\text{2(Br) = - 2}} \hfill \\
{\text{2(en)}}\,\,\,{\text{ = }}\,\,\,\,\,\,\,{\text{0}} \hfill \\
{\text{1(cr)}}\,\,\,\,\,{\text{ = }}\,\,\,{\text{ + 3}} \hfill \\
\end{gathered} \right\}{\text{ = + 1}}\]
Thus, complex ion is \(\left[\mathrm{Cr}(\mathrm{en})_{2} \mathrm{Br}_{2}\right]^{+}\).
Since anion is bromide thus, complex is
\(\left[\mathrm{Cr}(\mathrm{en})_{2} \mathrm{Br}_{2}\right] \mathrm{Br}\)