Number of moles = Mass ∕ Molar mass Given that the molar mass of oxygen O2 is 32.0g∕mol(2×16.0g∕mol), you can calculate the number of moles: Number of moles =3.0g∕32.0g∕mol=0.09375moles Rounded to four significant figures, the number of moles in 3.0 g of O 2 is approximately 0.0938 moles. Therefore, the closest answer choice is: 0.0930 moles.