In c2h4o2 there are
2 atoms of carbon
4 atoms of hydrogen
2 atoms of oxygen
Hydrogen atomic masses is 1 which was very low so 4 of them would still be the lowest mass percent. Then we have carbon and oxygen which both have 2 atoms. Oxygen atomic mass is more than carbon atomic mass, so oxygen should contribute more mass percent composition. The sequence from higher mass percent composition should be:
1. Oxygen
2. Carbon
3. Hydrogen
