The mean free path of CO under these new conditions is 52000 m ( = 5.2 x 104 m)

Rationale

The mean free path of molecules in the gas phase is inversely proportional to the pressure , hence when the pressure of the gas is reduced by 5 decades from 10-4 Torr to 10-9 Torr, the mean free path will increase by a factor of 100000.

i.e.   λ = 0.52 x 100000 = 5.2 x 104 m

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