\(\begin{array}{l}
4)\\
Mn{O_2} + 4HCl \to MnC{l_2} + C{l_2} + 2{H_2}O\\
C{l_2} + M \to MC{l_2}\\
nMC{l_2} = nC{l_2} = nMn{O_2} = \frac{{6,96}}{{87}} = 0,08\,mol\\
MMC{l_2} = \frac{{7,6}}{{0,08}} = 95g/mol\\
= > MM = 24g/mol\\
= > M:Mg\\
5)\\
2M + n{H_2}S{O_4} \to {M_2}{(S{O_4})_n} + n{H_2}\\
nM = 2n{M_2}{(S{O_4})_n}\\
= > \frac{{2,52}}{{MM}} = \frac{{6,84 \times 2}}{{2MM + 96n}}\\
= > MM = 28n\\
n = 2 = > MM = 56 = > M:Fe\\
6)\\
2M + n{H_2}S{O_4} \to {M_2}{(S{O_4})_n} + n{H_2}\\
nM = 2n{M_2}{(S{O_4})_n}\\
= > \frac{m}{{MM}} = \frac{{5m \times 2}}{{2MM + 96n}}\\
= > MM = 12n\\
n = 2 = > MM = 24 = > M:Mg
\end{array}\)
