\(M_{SO_3}=32+16.3=80g/mol\)
\(\%m_S=\dfrac{32}{80}.100\%=40\%\)
\(\%m_O=100\%-40\%=60\%\)
\(M_{Fe_2O_3}=56.2+16.3=160g/mol\)
\(\%m_{Fe}=\dfrac{56.2}{160}.100\%=70\%\)
\(\%m_O=100\%-70\%=30\%\)
\(M_{SO_2}=32+16.2=64g/mol\)
\(\%m_S=\dfrac{32}{64}.100\%=50\%\)
\(\%m_O=100\%-50\%=50\%\)