The osmotic pressure of a non-electrolytic solution can be calculated as follows,
π=CRT
π= osmotic pressure
C = molarity=VolumeofsolutioninLNumberofmoles
(1.29×10−3)=(MW)(0.3)0.63×(0.083)×300
MW=(0.3)×(1.29×10−3)0.63×0.083×300
=40534.88
≈40535 (Nearest integer)