The diameter of 4He atom is 1 Å. One mol of the gas occupies 20 litres at 20 K. The mean free path of the molecules will be, nearly {Given R = 8.4 J mol-1 K-1 and Avogadro number NA = 6 x 1023 mol-1}
1
7.5 × 10-7 m
2
3.25 × 10-7 m
3
1.5 × 10-7 m
4
4.9 × 10-7 m