Đáp án + giải thích các bước giải:
Ý thứ nhất :
\begin{array}{|c|c|c|}\hline \text{Chất}&\text{CTPT}\\\hline \text{muối ăn}&\text{NaCl}\\\hline \text{nước}&\text{}H_2O\\\hline \text{đường mía}&\text{}C_{12}H_{22}O_{11}\\\hline \text{khí cacbonic}&\text{}CO_2\\\hline\text{thuốc tím}&\text{}KMnO_4\\\hline\text{khí metan}&\text{}CH_4\\\hline\end{array}
Ý thứ hai :
\begin{array}{|c|c|c|}\hline \text{CTHH}&\text{NTK}\\\hline \text{Fe}&\text{56(đvC)}\\\hline \text{K}&\text{39(đvC)}\\\hline \text{Al}&\text{27(đvC)}\\\hline \text{Cu}&\text{64(đvC)}\\\hline\text{Ag}&\text{108(đvC)}\\\hline\end{array}