Đáp án đúng: C
Fe3O4.
TN1:
$\begin{array}{l}\overset{\text{+x}}{\mathop{\text{Fe}}}\,\xrightarrow{{}}\overset{\text{+3}}{\mathop{\text{Fe}}}\,\text{+(3-x)e}\\\text{1}\,\text{mol}\,\,\xrightarrow{{}}\,\,\,\,\,\text{(3-x)}\end{array}$
$\begin{array}{l}\overset{\text{+6}}{\mathop{\text{S}}}\,\,\,\text{+}\,\,\,\,\text{2e}\,\,\,\,\,\xrightarrow{{}}\,\,\,\,\overset{\text{+4}}{\mathop{\text{S}}}\,\\\,\,\,\,\,\,\,\,\,\text{(3-x)}\,\,\,\,\,\,\to \,\,\,\,\,\frac{\text{3-x}}{\text{2}}\end{array}$
TN2:
$\begin{array}{l}\text{Fe}\xrightarrow{{}}\overset{\text{+3}}{\mathop{\text{Fe}}}\,\text{+3e}\\\text{1}\,\text{mol}\,\,\xrightarrow{{}}\,\,\,\,\,3\end{array}$
$\begin{array}{l}\overset{\text{+6}}{\mathop{\text{S}}}\,\,\,\text{+}\,\,\,\,\text{2e}\,\,\,\,\,\xrightarrow{{}}\,\,\,\,\overset{\text{+4}}{\mathop{\text{S}}}\,\\\,\,\,\,\,\,\,\,\,\,\,\,\text{3}\,\,\,\,\,\,\,\,\to \,\,\,\,\,\,\,\,\,\,\frac{\text{3}}{\text{2}}\end{array}$
$\Rightarrow \frac{\text{3}}{\text{2}}\text{=9}\text{.}\frac{\text{3-x}}{\text{2}}\Rightarrow \text{x=}\frac{\text{8}}{\text{3}}\Rightarrow \text{F}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}}$
