What gas diffuses faster helium or neon?

The correct answer is helium.

For Neon (Ne), the atomic mass is 10 daltons, so the molar mass is 10

grams. This means that one mole (Avogadro's number of particles, 6.02

x 10^23) has a mass of 10 grams. Hydrogen, with an atomic mass of

1 dalton for it's single proton, the molar mass would be 1 gram. With

Neon, the speed of the individual Neon atoms is

proportional to 1 / sqrt (10). So it is helium.