Đáp án đúng: C
Fe2O3.
$\begin{array}{l}F{{e}_{x}}{{O}_{y}}+yCO\xrightarrow{{}}xFe+yC{{O}_{2}}\\0,1\,mol\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,0,3\,mol\\\Rightarrow \,0,1.y=0,3\,\Rightarrow y=3\\\Rightarrow F{{e}_{2}}{{O}_{3}}\end{array}$