Em tham khảo nha:

\(\begin{array}{l}
1)\\
R + 2HCl \to RC{l_2} + {H_2}\\
P1:V{H_2} > 3,36l \Rightarrow n{H_2} > \dfrac{{3,36}}{{22,4}} = 0,15\,mol\\
 \Rightarrow nR > 0,15\,mol \Rightarrow MR < \dfrac{{4,8}}{{0,15}} = 32g/mol(1)\\
{P_2}:V{H_2} < 6,72l \Rightarrow n{H_2} < \dfrac{{6,72}}{{22,4}} = 0,3\,mol\\
 \Rightarrow nR < 0,3\,mol \Rightarrow MR > \dfrac{{4,8}}{{0,3}} = 16g/mol(2)\\
(1),(2) \Rightarrow MR = 24g/mol \Rightarrow R:Magie(Mg)\\
2)\\
2R + {O_2} \to 2RO\\
P1:V{O_2} = 2,016l \Rightarrow n{O_2} = \dfrac{{2,016}}{{22,4}} = 0,09\,mol\\
 \Rightarrow nR > 0,09 \times 2 = 0,18\,mol \Rightarrow MR < \dfrac{{4,8}}{{0,18}} = 26,67g/mol(1)\\
{P_2}:V{O_2} = 2,688l \Rightarrow n{O_2} = \dfrac{{2,688}}{{22,4}} = 0,12\,mol\\
 \Rightarrow nR < 0,12 \times 2 = 0,24\,mol \Rightarrow MR > \dfrac{{4,8}}{{0,24}} = 20g/mol(2)\\
(1),(2) \Rightarrow MR = 24g/mol \Rightarrow R:Magie(Mg)
\end{array}\)