Đáp án đúng: C
Fe2O3.
Xét trường hợp tạo 2 muối $\text{BaC}{{\text{O}}_{\text{3}}}\text{,}\,\text{Ba(HC}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}$
$\begin{array}{l}\xrightarrow{\text{BTNT}\,\,\text{Ba}}\,{{\text{n}}_{\text{Ba(HC}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}}}\text{=}{{\text{n}}_{\text{Ba(OH}{{\text{)}}_{\text{2}}}}}\text{-}{{\text{n}}_{\text{BaC}{{\text{O}}_{\text{3}}}}}\text{=0,1-0,05=0,05}\\\xrightarrow{\text{BTNT}\,\text{C}}\,{{\text{n}}_{\text{C}{{\text{O}}_{\text{2}}}}}\text{=}{{\text{n}}_{\text{BaC}{{\text{O}}_{\text{3}}}}}\text{+2}{{\text{n}}_{\text{Ba(HC}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}}}\text{=0,15}\,\text{mol}\\\Rightarrow {{\text{n}}_{\text{O}\,\,\text{(oxit)}}}\,\text{=}\,{{\text{n}}_{\text{C}{{\text{O}}_{\text{2}}}}}\,\text{=}\,\text{0,15}\,\text{mol}\,\Rightarrow \,{{\text{n}}_{\text{C}{{\text{l}}^{\text{-}}}}}\,\text{=}\,\text{2}{{\text{n}}_{\text{O}\,}}\text{=}\,\text{0,3}\,\text{mol}\\{{\text{n}}_{\text{Fe}}}\text{=}{{\text{n}}_{\text{FeC}{{\text{l}}_{\text{2}}}}}\text{=}\frac{\text{12,7}}{\text{127}}\text{=0,1}\,\text{mol}\,\Rightarrow \frac{\text{y}}{\text{x}}\text{=}\frac{{{\text{n}}_{\text{O}}}}{{{\text{n}}_{\text{Fe}}}}\text{=}\frac{\text{0,15}}{\text{0,1}}\text{=}\frac{\text{3}}{\text{2}}\Rightarrow \text{F}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}\end{array}$
Xét trường hợp tạo kết tủa và dư$\text{Ba(OH}{{\text{)}}_{\text{2}}}$, tính như trên và chứng minh không thỏa mãn.
