Question: how many grams of oxygen are in a liter?
Answer: D. At STP (standard temperature and pressure), an ideal gas occupies 22.4 liters per mole. Here we have 48 g of oxygen gas or O2, each molecule of which consists of two atoms of the oxygen element. Since oxygen (O) has an atomic mass of 16 g, oxygen gas (O2) has a molecular mass of 2 x 16 = 32 g.