\(\left[Br_2\right]=\left[Cl_2\right]=\dfrac{4}{1}=4\left(M\right)\)
\(K_C=\dfrac{\left[Br_2\right].\left[Cl_2\right]}{\left[BrCl\right]^2}=11,1\)
\(\Leftrightarrow\dfrac{4^2}{\left[BrCl\right]^2}=11,1\\ \Rightarrow\left[BrCl\right]=1,2\left(M\right)\)
