• Root mean squared or RMS can be calculated using the provided temperature and the molar mass of the gas where:

• We need the molar mass in kg/mol instead of g/mol because we have a unit J which can be simplified as kg²•m²•s^-2
• Molar mass of F₂, Cl₂ and Br₂ in kg/mol will appear as:

1 g = 1x10^-3 kg/mol

MM of F₂ : 19.0 (2) = 38 g/mol or 38x10^-3 kg/mol

MM of Cl₂ : 35.45 (2) = 70.90 g/mol or 70.90x10^-3 kg/mol

MM of Br₂ : 79.90 (2) = 159.8 g/mol or 159.8x10^-3 kg/mol