For helium gas, vanderWaal constant, b=0.024Lmol-. Calculate the molecular diameter((A∘) of helium gas.

1 Mol of He -gas= Avogadro no.N=6.023×1023mol−volume of one molecule of gas=43πr3 volume of one mole of gas =6.023×1023×43πr3b=0.024Lmol−  = 0.024×1000=24cm3mol−We know that : b =4×[Volume occupied by molecules present in one mol of gas ] ∴24 =4×N×43πr3=4×6.023×1023mol−×43×227×r3∴ r=24cm3mol−×3×74×6.023×1023mol−×4×2213∴ =2.377×10−24cm313=1.33×10−8cm=1.33A∘But Diameter = 2 r.So, diameter=2×1.33A∘=2.66A∘