Em tham khảo nha :

Câu b : hỗn hợp B có thể tích là 2,8l

\(\begin{array}{l}
a)\\
{M_A} = 0,3875{M_{{O_2}}} = 12,4dvC\\
hh:{N_2}(a\,mol);{H_2}(b\,mol)\\
\dfrac{{28a + 2b}}{{a + b}} = 12,4\\
 \Rightarrow \dfrac{a}{b} = \dfrac{{12,4 - 2}}{{28 - 12,4}} = \dfrac{2}{3}\\
\% {V_{{N_2}}} = \dfrac{2}{{2 + 3}} \times 100\%  = 40\% \\
\% {V_{{H_2}}} = 100 - 40 = 60\% \\
b)\\
{V_{{N_2}}} = \dfrac{{5 \times 40}}{{100}} = 2l\\
{V_{{H_2}}} = 5 - 2 = 3l\\
{N_2} + 3{H_2} \to 2N{H_3}\\
\dfrac{2}{1} > \dfrac{3}{3} \Rightarrow {N_2}\text{ dư}\\
{V_{{N_2}d}} = {V_{{N_2}}} - \dfrac{1}{3}{V_{{H_2}}} = 1l\\
{V_{N{H_3}}} = \frac{2}{3}{V_{{H_2}}} = 2l\\
{V_{N{H_3}}} = 2,8 - 1 = 1,8l\\
H = \dfrac{{1,8}}{2} \times 100\%  = 90\% 
\end{array}\)