Select the answer which shows the correct order, slowest to fastest, of the relative rate of diffusion of the gases.
kr, ar, ne, n
n, ne, ar, kr
kr, ne, n, ar
ne, ar, n, kr

The heavier the gas is, the slower the gas will diffuse.  the correct order is Kr, Ar, Ne, N based off of the atomic weight.  However I don't think N is a gas.  Nitrogen is diatomic so it should be N₂.

I hope this helps. 

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