Đáp án:

 Đề là cho V lít oxi với 20l hỗn hợp A nha em

Giải thích các bước giải:

\(\begin{array}{l}
{M_A} = 16 \times 3 = 48\,g/mol\\
{M_B} = 16 \times 2,5 = 40g/mol\\
\text{ Theo phương pháp đường chéo ta có }\\
{M_{{O_2}}} = 32\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,8\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \searrow \,\,\,\,\,\,\,\,\,\,\,\, \nearrow \\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,40\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \nearrow \,\,\,\,\,\,\,\,\,\,\,\, \searrow \\
{M_A} = 48\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,8\\
 \Rightarrow \dfrac{{{V_{{O_2}}}}}{{{V_A}}} = \dfrac{8}{8} = \dfrac{1}{1} \Rightarrow {V_{{O_2}}} = {V_A} = 20l\,
\end{array}\)