Em tham khảo nha:
\(\begin{array}{l}
a)\\
{n_{Fe}} = {n_{Mg}} = a\,mol \Rightarrow 56a + 24a = 12\\
\Rightarrow a = 0,15\,mol\\
\% {m_{Fe}} = \dfrac{{0,15 \times 56}}{{12}} \times 100\% = 70\% \\
\% {m_{Mg}} = 100 - 70 = 30\% \\
b)\\
{n_{hh}} = \dfrac{{4,48}}{{22,4}} = 0,2\,mol\\
{n_{C{O_2}}} = \dfrac{{0,2}}{{7 + 3}} \times 7 = 0,14\,mol\\
{n_{{O_2}}} = 0,2 - 0,14 = 0,06\,mol\\
\% {m_{C{O_2}}} = \dfrac{{0,14 \times 44}}{{0,14 \times 44 + 0,06 \times 32}} \times 100\% = 76,24\% \\
\% {m_{{O_2}}} = 100 - 76,24 = 23,76\% \\
c)\\
{n_{hh}} = \dfrac{{11,2}}{{22,4}} = 0,5\,mol\\
{n_{N{O_2}}} = \dfrac{{0,5}}{{2 + 3}} \times 2 = 0,2\,mol\\
{n_{{O_2}}} = 0,5 - 0,2 = 0,3\,mol\\
\% {m_{N{O_2}}} = \dfrac{{0,2 \times 46}}{{0,2 \times 46 + 0,3 \times 32}} \times 100\% = 48,94\% \\
\% {m_{{O_2}}} = 100 - 48,94 = 51,06\%
\end{array}\)
