the phenomemenon can be explained by the Graham's law of diffusion.
Graham's law of difussion states that the rate of difussion is inversely proportional to the square root of the molecular mass,which means the gas with lower molecular mass will escape faster.
Helium gas has a molecular mass of 4 while Neon has a molecular mass of 10.
rate of diffusion of He/rate of difussion of Ne=√4/10=√0.4=0.63
It means He(g) will move 0.63 times faster than Ne(g) under the same condition
