Đáp án đúng: B
54%.
$\begin{array}{l}\text{Na}\,\xrightarrow{{}}\,\text{NaOH}\\\,\,\text{x}\,\,\,\,\xrightarrow{{}}\,\,\,\,\text{x}\,\,\text{mol}\\\text{Al +}\,\text{NaOH}\,\text{+}\,\text{3}{{\text{H}}_{\text{2}}}\text{O}\,\xrightarrow{{}}\,\text{NaAl(OH}{{\text{)}}_{\text{4}}}\,\text{+}\,\frac{\text{3}}{\text{2}}{{\text{H}}_{\text{2}}}\\\,x\,\,\leftarrow \,\,\,x\,mol\\\Rightarrow \,{\scriptstyle{}^{o}\!\!\diagup\!\!{}_{o}\;}Al\,=\,\frac{27x}{27x+23x}=54{\scriptstyle{}^{o}\!\!\diagup\!\!{}_{o}\;}\end{array}$
