The molar mass of CO₂ is calculated from the atomic masses of carbon (C) and oxygen (O₂) atoms. The atomic mass of carbon is ~12.01 g/mol and that of one oxygen is ~16.00 g/mol. CO₂ contains one carbon and 2 oxygen atoms, so the molar mass = 12.01 + (2 × 16.00) = 44.01 g/mol.