Consider the following statements regarding osmotic pressure:

(A) Molar mass of a protein can be determined using the osmotic pressure method.
(B) The osmotic pressure is proportional to the molarity.
(C) Reverse osmosis occurs when a pressure larger than osmotic pressure is applied to the concentrated solution side.
(D) Edema occurs due to retention of water in tissue cells as a result of osmosis.

Choose the correct statements with reference to osmotic pressure:

The correct option is (A), (B), (C) and (D).

Let us analyze each statement step-by-step to understand why all of them are correct:

Statement (A): Molar mass of a protein can be determined using the osmotic pressure method.
Osmotic pressure measurement is exceptionally useful for determining the molar masses of biomolecules, polymers, and proteins. Unlike other colligative properties, osmotic pressure measurements are carried out at room temperature, and the magnitude of osmotic pressure is relatively large even for very dilute solutions. Since proteins are unstable at higher temperatures and have low solubility, the osmotic pressure method is the preferred technique for determining their molar mass.

Statement (B): The osmotic pressure is proportional to the molarity.
For a dilute solution, osmotic pressure ($\pi$) is given by the equation:
$\pi =CRT$
where $C$ is the concentration of the solution in molarity (moles per liter), $R$ is the gas constant, and $T$ is the temperature. This equation shows that at a constant temperature, osmotic pressure is directly proportional to the molarity ($C$) of the solution.

Statement (C): Reverse osmosis occurs when a pressure larger than osmotic pressure is applied to the concentrated solution side.
If a pressure greater than the osmotic pressure is applied to the concentrated solution side, the direction of osmosis is reversed. That is, the pure solvent starts flowing out of the solution through the semipermeable membrane. This process is called reverse osmosis and is widely used for the desalination of seawater.

Statement (D): Edema occurs due to retention of water in tissue cells as a result of osmosis.
When people consume a lot of salt or salty food, they experience water retention in tissue cells and intercellular spaces due to osmosis. The resulting puffiness or swelling is medically referred to as edema.

Since all four statements (A), (B), (C), and (D) are correct, the correct choice is (A), (B), (C) and (D).