Someone answer this please.

The percent composition of oxygen is 54.5%

Explanation:

Below I have attached my work through, but essentially the percent composition relies on finding the mass of the oxygens and dividing it by the mass of the whole compound. The masses of the elements can be found on the periodic table and added together to get a mass of the whole compound- ascorbic acid. Then, you turn this proportion into a percent by multiplying by 100%.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.