We know that, exclused volume 'b' is given as :
b=4× volume occupied by the molecules in one mole of a gas
=4×N0×(43πr3)
3.22×10−5=4×6.02×1023×43×227×r3
or r=(3.22×10−5×3×74×6.02×1023×4×22)
=0.1472×10−9 m
∴ Diameter =2r=2×0.1472×10−9
=0.2944×10−9 m=0.2944 nm