Đáp án đúng: D
V2 : V1 = 7 : 10.
Phương trình phản ứng
$\begin{array}{l}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{C}_{3}}{{H}_{8}}\,\,\,+\,\,\,\,\,5{{O}_{2}}\,\,\,\xrightarrow{{{t}^{o}}}\,\,\,\,\,3C{{O}_{2}}\,\,\,\,\,\,\,+\,\,\,\,\,\,4{{H}_{2}}O\,\,\,\,\,\,\,\,\,(1)\\Trc\,(lit):\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\to \,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\\Pu\,(lit):\,\,\,\,\,\,\,\,\frac{x}{5}\,\,\,\,\,\,\,\leftarrow \,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\to \,\,\,\,\,\,\,\,\,\,\,\frac{3x}{5}\,\,\,\,\,\,\,\,\,\,\to \,\,\,\,\,\,\frac{4x}{5}\\Sau\,(lit):\,\,\,\,\,\frac{4x}{5}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,0\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{3x}{5}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{4x}{5}\end{array}$
Sau phản ứng hơi nước bị ngưng tụ nên hỗn hợp khí còn lại gồm C3H8 và O2 dư. Ta có :
${{V}_{1}}={{V}_{C{}_{3}{{H}_{8}}}}+{{V}_{{{O}_{2}}}}=2x\,\,\,l\acute{i}t;\,\,{{V}_{2}}={{V}_{C{}_{3}{{H}_{8}}\,\,spu}}+{{V}_{C{{O}_{2}}}}=\frac{4x}{5}\,+\frac{3x}{5}=\frac{7x}{5}\,\,l\acute{i}t\\\Rightarrow \frac{{{V}_{2}}}{{{V}_{1}}}=\frac{7}{10}.$
