#### Answer

The percent composition of oxygen in acetic acid is equal to $53.29\%$.

#### Work Step by Step

1. Calculate the molar mass of: $C_2H_4O_2$:
Molar Mass ($C_2H_4O_2$):
12.01* 2 + 1.008* 4 + 16.00* 2 = 60.05g/mol
2. Calculate the total mass of $O$ in one mole of this compound:
Total Mass ($O$): $ 2 \times 16.00 = 32.00$
3. Find the mass percent composition:
$\frac{Total-mass (O)}{Molar-Mass} \times 100\% = \frac{ 32.00}{ 60.05} \times 100\% = 53.29\%$