a, \(CH_2=CH_2+Br_2\rightarrow CH_2Br-CH_2Br\)
b, \(n_{C_2H_4Br_2}=\dfrac{9,4}{188}=0,05\left(mol\right)\)
Theo PT: \(n_{C_2H_4}=n_{C_2H_4Br_2}=0,05\left(mol\right)\)
\(\Rightarrow\left\{{}\begin{matrix}\%V_{C_2H_4}=\dfrac{0,05.22,4}{2,8}.100\%=40\%\\\%V_{CH_4}=60\%\end{matrix}\right.\)