Ethane-1,2-diol is used as antifreeze and propane-1,2,3-triol as a moisturiser…

Step 1. Formulas. Ethane-1,2-diol is $\text{C}_{2}\text{H}_{6}\text{O}_{2}$. Propane-1,2,3-triol is $\text{C}_{3}\text{H}_{8}\text{O}_{3}$.

Step 2. Ethane-1,2-diol. Molar mass: $2 \times 12.011 + 6 \times 1.008 + 2 \times 15.999 = 62.07\ \text{g/mol}$. Oxygen: $\dfrac{2 \times 15.999}{62.068} \times 100 = 51.55\ \%$.

Step 3. Propane-1,2,3-triol. Molar mass: $3 \times 12.011 + 8 \times 1.008 + 3 \times 15.999 = 92.094\ \text{g/mol}$. Oxygen: $\dfrac{3 \times 15.999}{92.094} \times 100 = 52.12\ \%$.