To find the percent composition of Carbon in a substance, you need to calculate the percent of the total mass that is made up of Carbon.
The first step is to add up the masses of all the elements in the substance to get the total mass:
2.59 g Carbon + 39.56 g Sulfur + 43.03 g Oxygen = 85.18 g
Next, divide the mass of Carbon by the total mass and multiply by 100 to get the percent of the total mass that is Carbon:
(2.59 g Carbon / 85.18 g) * 100 = 3.03% Carbon
So, the percent composition of Carbon in the substance is 3.03%.