Em tham khảo nha :
\(\begin{array}{l}
a)\\
Mg + {X_2} \to Mg{X_2}\\
{n_{Mg}} = \dfrac{{1,2}}{{24}} = 0,05mol\\
{n_{{X_2}}} = {n_{Mg}} = 0,05mol\\
{M_{{X_2}}} = \dfrac{8}{{0,05}} = 160dvC\\
\Rightarrow {M_X} = \frac{{160}}{2} = 80dvC\\
\Rightarrow X:Brom(Br)\\
b)\\
2Al + 3{X_2} \to 2Al{X_3}\\
{n_{{X_2}}} = \dfrac{{6,72}}{{22,4}} = 0,3mol\\
{n_{Al{X_3}}} = \dfrac{2}{3}{n_{{X_2}}} = 0,2mol\\
{M_{Al{X_3}}} = \dfrac{{26,7}}{{0,2}} = 133,5dvC\\
\Rightarrow {M_X} = \dfrac{{133,5 - 27}}{3} = 35,5dvC\\
\Rightarrow X:Clo(Cl)
\end{array}\)
