Đáp án đúng: A
x =a+b0,2
$\begin{array}{l}\text{B}{{\text{a}}^{\text{2+}}}\,\xrightarrow{\text{HCO}_{\text{3}}^{\text{-}}\text{,}\,\text{CO}_{\text{3}}^{\text{2-}}\text{,}\,\text{SO}_{\text{4}}^{\text{2-}}}\,\text{BaC}{{\text{O}}_{\text{3}}}\text{,}\,\text{BaS}{{\text{O}}_{\text{4}}}\\\Rightarrow \,{{\text{n}}_{\text{B}{{\text{a}}^{\text{2+}}}}}\,\text{=}\,{{\text{n}}_{\text{HCO}_{\text{3}}^{\text{-}}}}\,\text{+}\,{{\text{n}}_{\text{CO}_{\text{3}}^{\text{2-}}}}\,\text{+}\,{{\text{n}}_{\text{SO}_{\text{4}}^{\text{2-}}}}\,\Rightarrow \,\text{0}\text{,1x}\,\text{=}\,\text{b}\,\text{+}\,\text{c}\,\text{+}\,\text{d}\\\Rightarrow \,\text{0}\text{,1x}\,\text{=}\,\text{b}\,\text{+}\,\frac{\text{a}\,\text{-}\,\text{b}}{\text{2}}\,\Rightarrow \,\text{x}\,\text{=}\,\frac{\text{a}\,\text{+}\,\text{b}}{\text{0}\text{,2}}\end{array}$
