Answer:
He
Step-by-step explanation:
A postulate of the Kinetic Molecular Theory is that at a given temperature, the average kinetic energy of the molecules is directly proportional to the Kelvin temperature.
KE = ½ mv² ∝ T
mv² ∝ T Divide each side by T
v² ∝ T/m
If T is constant.
v² ∝ 1/m Take the square root of each side
v ∝ 1/√m
This is an inverse relationship, so the molecules with the smallest molecular mass should have the highest average speeds.
A helium molecule has the smallest mass, so helium has the highest average molecular velocity.
