Đáp án đúng: A
x = 5y.
$\text{Al}\,\xrightarrow{{}}\,\text{A}{{\text{l}}^{\text{3+}}}\,\text{+}\,\text{3e}$
$\begin{array}{l}\text{2}{{\text{H}}^{\text{+}}}\,\text{+}\,\text{2e}\,\xrightarrow{{}}\,{{\text{H}}_{\text{2}}}\\\text{12}{{\text{H}}^{\text{+}}}\,\text{+}\,\text{2NO}_{\text{3}}^{\text{-}}\,\text{+}\,\text{10e}\,\xrightarrow{{}}\,{{\text{N}}_{\text{2}}}\,\text{+}\,6{{\text{H}}_{\text{2}}}\text{O}\end{array}$
Bảo toàn e có$\text{2}{{\text{n}}_{{{\text{H}}_{\text{2}}}}}\,\text{=}\,\text{3}{{\text{n}}_{\text{Al}}}\,\text{=}\,\text{10}{{\text{n}}_{{{\text{N}}_{\text{2}}}}}\,\Rightarrow \,\text{2x}\,\text{=}\,\text{10y}\,\,\text{hay}\,\,\text{x}\,\text{=}\,\text{5x}$