What is the percent of oxygen by mass in C2H4O2? (H:1.00 amu, C: 12.01 amu, O:16.00 amu)

Explanation:

Molar mass of all the elements are given in small below the name of that element. Eg. For C, molar mass 12.011 gm etc.

So, molar mass of C2H4O2 = (2× 12.011)+(4×1.008)+(2×15.999) = 60.052 gm

Now molar mass of O present in this molecule= 2×15.999 =31.998 gm

60.052 gm molecule contain 31.998 gm oxygen

So, 100 gm molecule contains (31.998/60.052)×100 gm = 53.28 %