Mong mn giúp em câu này ạ

Em tham khảo nha:

\(\begin{array}{l}
a)\\
{C_2}{H_4} + B{r_2} \to {C_2}{H_4}B{r_2}\\
{n_{B{r_2}}} = 0,15 \times 0,4 = 0,06\,mol\\
{n_{{C_2}{H_4}}} = {n_{B{r_2}}} = 0,06\,mol\\
\% {m_{{C_2}{H_4}}} = \dfrac{{0,06 \times 28}}{{2,58}} \times 100\%  = 65,12\% \\
\% {m_{{C_2}{H_6}}} = 100 - 65,12 = 34,88\% \\
b)\\
{m_{{C_2}{H_6}}} = 2,58 - 0,06 \times 28 = 0,9g\\
{n_{{C_2}{H_6}}} = \dfrac{{0,9}}{{30}} = 0,03\,mol\\
\% {V_{{C_2}{H_4}}} = \dfrac{{0,06}}{{0,06 + 0,03}} \times 100\%  = 66,67\% \\
\% {V_{{C_2}{H_6}}} = 100 - 66,67 = 33,33\% 
\end{array}\)