Đáp án đúng: D 2,94 gam. $\begin{array}{l}\text{6FeS}{{\text{O}}_{\text{4}}}\text{+}{{\text{K}}_{\text{2}}}\text{C}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}\text{+7}{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\xrightarrow{{}}\text{3F}{{\text{e}}_{\text{2}}}{{\text{(S}{{\text{O}}_{\text{4}}}\text{)}}_{\text{3}}}\text{+C}{{\text{r}}_{\text{2}}}{{\text{(S}{{\text{O}}_{\text{4}}}\text{)}}_{\text{3}}}\text{+}{{\text{K}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{+7}{{\text{H}}_{\text{2}}}\text{O}\\\,\text{0,06}\,\xrightarrow{{}}\,\text{0,01}\\\Rightarrow {{\text{m}}_{{{\text{K}}_{\text{2}}}\text{C}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}}}\text{=2,94}\,\text{gam}\text{.}\end{array}$
