$\text{Đáp án + giải thích các bước giải :}$

$Gọi$ $V_{\text{hỗn hợp 1}}$ $=$ $V_{\text{hỗn hợp 2}}$ $=$ $22,4$ $(lít)$

$+$ $hỗn$ $hợp$ $1$ $:$

$V_{CH_4}$ $=$ $22,4$ $×$ $25\%$ $=$ $5,6$ $(lít)$

$⇒$ $n_{CH_4}$ $=$ $\frac{5,6}{22,4}$ $=$ $0,25$ $(mol)$

$V_{C_3H_8}$ $=$ $22,4$ $×$ $75\%$ $=$ $16,8$ $(lít)$

$⇒$ $n_{C_3H_8}$ $=$ $\frac{16,8}{22,4}$ $=$ $0,75$ $(mol)$

$⇒$ $\overline{M}_{\text{hỗn hợp 1}}$ $=$ $\frac{m_{CH_4}+m_{C_3H_8}}{n_{CH_4}+n_{C_3H_8}}$ 

$⇒$ $\overline{M}_{\text{hỗn hợp 1}}$ $=$ $\frac{0,25×16+0,75×44}{0,25+0,75}$ 

$⇒$ $\overline{M}_{\text{hỗn hợp 1}}$ $=$ $37$ 

$+$ $hỗn$ $hợp$ $2$ $:$

$V_{H_2}$ $=$ $22,4$ $×$ $40\%$ $=$ $8,96$ $(lít)$

$⇒$ $n_{H_2}$ $=$ $\frac{8,96}{22,4}$ $=$ $0,4$ $(mol)$

$V_{O_2}$ $=$ $22,4$ $×$ $75\%$ $=$ $13,44$ $(lít)$

$⇒$ $n_{O_2}$ $=$ $\frac{13,44}{22,4}$ $=$ $0,6$ $(mol)$

$⇒$ $\overline{M}_{\text{hỗn hợp 2}}$ $=$ $\frac{m_{H_2}+m_{O_2}}{n_{H_2}+n_{O_2}}$ 

$⇒$ $\overline{M}_{\text{hỗn hợp 2}}$ $=$ $\frac{0,4×2+0,6×32}{0,4+0,6}$ 

$⇒$ $\overline{M}_{\text{hỗn hợp 2}}$ $=$ $20$ 

$⇒$ $d_{\frac{\text{hỗn hợp 1}}{\text{hỗn hợp 2}}}$ $=$ $\frac{37}{20}$ $=$ $1,85$

$\text{Chúc bn hk tốt !! :))))}$

\(\begin{array}{l}
Gia\,su\,n_{hh\,1}=n_{hh\,2}=10(mol)\\
\to \begin{cases} n_{CH_4}=10.25\%=2,5(mol)\\  n_{C_3H_8}=10-2,5=7,5(mol)\\ n_{H_2}=10.40\%=4(mol)\\ n_{O_2}=10-4=6(mol) \end{cases}\\
\to \begin{cases}\overline{M_A}=\dfrac{2,5.16+7,5.44}{10}=37(g/mol)\\ \overline{M_B}=\dfrac{4.2+6.32}{10}=20g/mol) \end{cases}\\
\to d_{A/B}=\dfrac{37}{20}=1,85
\end{array}\)