Đáp án đúng: A
ankan
$\begin{array}{l}{{C}_{x}}{{H}_{y}}\,+\,(x+\frac{y}{4}){{O}_{2}}\,\xrightarrow{{{t}^{o}}}\,xC{{O}_{2}}\,+\,\frac{y}{2}{{H}_{2}}O\\\Rightarrow \,\frac{{{n}_{{{H}_{2}}O}}}{{{n}_{C{{O}_{2}}}}}\,=\,\frac{y}{2x}\end{array}$
Xét đồng đẳng kế tiếp của CxHy là Cx+1Hy+2
$\displaystyle \begin{array}{l}\Rightarrow \,\frac{n_{{{H}_{2}}O}^{'}}{n_{C{{O}_{2}}}^{'}}\,=\,\frac{y+2}{2(x+1)}\,<\,\frac{y}{2x}\,\Rightarrow \,2xy\,+\,4x\,<\,2xy\,+\,2y\,\\\Rightarrow \,2x\,<\,y\,\Rightarrow \,ankan\end{array}$
