Answer : 0.125 M
Explanation : The definition of osmotic pressure is "the pressure can be applied on a pure solvent to prevent it passing into a given solution by osmosis".
So according to this definition, osmotic pressure can be called as directly proportional to the concentration of the solution and hence the pressure can also be directly proportional to the concentration.
Hence, if pressure is getting decreased from 28 to 7 it means it got decreased by 4 times;
28 / 7 = 4 that means;
So the concentration will be also decreased by 4 times so, 0.50 / 4 = 0.125 M