Pressure: 1 atm
Temperature: 273 K

@STP, 1 mole of gas occupies 22.4 L

Kinetic energy of an ideal gas is proportional to its absolute temperature. Identity of gas doesn matter; only temperature matters.

Ideal gas equation: PV = nRT

PV/T = PV/T

r₁/r₂ = sqr(M₂/M₁)