Đáp án:

 a) C2H4: 16,8 g; CH4: 4,8 g

b) 1M

Giải thích các bước giải:

a) 

$\begin{gathered}
  {n_{hh}} = \dfrac{{20,16}}{{22,4}} = 0,9mol;{n_{B{r_2}}} = 0,3.2 = 0,6mol \hfill \\
  {C_2}{H_4} + B{r_2} \to {C_2}{H_4}B{r_2} \hfill \\
   \Rightarrow {n_{{C_2}{H_4}}} = {n_{B{r_2}}} = 0,6mol \hfill \\
   \Rightarrow {n_{C{H_4}}} = 0,9 - 0,6 = 0,3mol \hfill \\
   \Rightarrow {m_{{C_2}{H_4}}} = 0,6.28 = 16,8\left( g \right);{m_{C{H_4}}} = 0,3.16 = 4,8\left( g \right) \hfill \\ 
\end{gathered} $ 

b) 

$\begin{gathered}
  {n_{{C_2}{H_2}}} = \dfrac{{8,96}}{{22,4}} = 0,4mol \hfill \\
  {C_2}{H_2} + 2B{r_2} \to {C_2}{H_4}B{r_4} \hfill \\
  \dfrac{{{n_{{C_2}{H_2}}}}}{1} = 0,4 > \dfrac{{{n_{B{r_2}}}}}{2} = 0,3 \hfill \\ 
\end{gathered} $

⇒ ${C_2}{H_2}$ dư, $B{r_2}$ hết

${n_{{C_2}{H_2}B{r_4}}} = \dfrac{1}{2}{n_{B{r_2}}} = 0,3mol \Rightarrow {C_{Mdd}} = \dfrac{{0,3}}{{0,3}} = 1M$