[tex]M_{SO_2}=32+(2*16)=32+32=64\ g/mol \\ S:O=32:32=1:1\\ \\ S=\frac{32*100}{64}=50\% \\ O=\frac{(2*16)*100}{64}=\frac{3200}{64}=50\%[/tex]
[tex]M_{H_3PO_4}=(3*1)+31+(4*16)=3+31+64=98\ g/mol \\ H:P:O=3:31:64 \\ \\ H=\frac{(3*1)*100}{98}=\frac{300}{98}=3,06\% \\ \\ P=\frac{31*100}{98}=31,63\% \\ \\ O=\frac{(4*16)*100}{98}=\frac{6400}{98}=65,30\%[/tex]
[tex]M_{Mg(OH)_2}=24+(2*17)=24+34=58\ g/mol \\ Mg:O:H=24:32:2=12:16:1 \\ \\ Mg=\frac{24*100}{58}=41,37\% \\ \\ O=\frac{(2*16)*100}{58}=\frac{3200}{58}=55,17\% \\ \\ H=\frac{200}{58}=3,44\%[/tex]