To determine the mass of 1 mol of O2 gas, we need to consider the molar mass of O2. The molar mass of a substance is the mass of one mole of that substance, expressed in grams.

The molecular formula of oxygen gas is O2, which means that one molecule of oxygen consists of two oxygen atoms. The molar mass of oxygen is approximately 32 grams per mole (g/mol). This value is calculated by adding the atomic masses of the two oxygen atoms in the molecule.

Therefore, 1 mol of O2 gas has a mass of approximately 32 grams.