Đáp án đúng: B
Na2CO3.
$\displaystyle \begin{array}{l}\text{BaO}\xrightarrow{{}}\text{Ba(OH}{{\text{)}}_{\text{2}}}\\\text{Ba(OH}{{\text{)}}_{\text{2}}}\text{+N}{{\text{H}}_{\text{4}}}\text{HC}{{\text{O}}_{\text{3}}}\xrightarrow{{}}\text{BaC}{{\text{O}}_{\text{3}}}\text{+N}{{\text{H}}_{\text{3}}}\text{+2}{{\text{H}}_{\text{2}}}\text{O}\\\,\,\,\,\,\,\,\,\text{4}\,\,\,\,\,\,\leftarrow \,\,\,\,\,\,\,\text{4}\,\,\text{mol}\\\text{Ba(OH}{{\text{)}}_{\text{2}}}\text{+2NaHC}{{\text{O}}_{\text{3}}}\xrightarrow{{}}\text{BaC}{{\text{O}}_{\text{3}}}\text{+N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\text{+2}{{\text{H}}_{\text{2}}}\text{O}\\\,\,\,\,\,\,\,\,\text{1}\,\,\,\,\,\,\,\,\,\leftrightarrow \,\,\,\,\,\text{2}\,\,\,\text{mol}\end{array}$Y chỉ gồm Na2CO3
