136. Solving a chemistry problem

Below are the results of studying the equilibrium distribution of selenium hydrosol particles in height under the action of gravity (at 293 K):
h, µm 500 850 1050 1250
Number of particles per unit volume 595 271 165 90
Using this data, calculate the diffusion coefficient of selenium particles in water. Take selenium density equal to 4.81 g/cm3, water density 1 g/cm3, water viscosity 1⋅10-3 Pa⋅s.