Osmotic Pressure `(pi)`.

Explanation

Osmosis is the phenomenon of spontaneous flow of the solvent molecules through a semipermeable membrane from pure solvent to solution or from a dilute solution to concentrated solution. It was first observed by Abbe Nollet.
Osmosis may be
(i) Exosmosis : It is outward flow of water or solvent from a cell through semipermeable membrane.
(ii) Endosmosis : It is inward flow of water or solvent from a cell through a semipermeable membrane. The hydrostatic pressure developed on the solution which just prevents the osmosis of pure solvent into the solution through a semipermeable membrane is called
Osmotic pressure `(pi) =RCT , (C=n_B /V =(W_B)/(M_BV))`
`M_B = (W_BRT)/(piV)`
`pi = (dRT)/(M_B), (d=W_B/V)`
where, d = density, R = solution constant, T = temperature, `M_B` = molar mass of solute.