Arrange the following steps in the correct sequence to carry out reverse osmosis

(A) Two solutions having different concentrations of the same solute are taken.
(B) Very high external pressure is applied on the high concentration side.
(C) A semipermeable membrane is inserted between the two solutions.
(D) Solvent flows from the high concentration side to the low concentration one.

Choose the correct answer from the options given below:

(A), (C), (B), (D)

The correct answer is Option (2) → (A), (C), (B), (D)

To understand the sequence, we must look at how the physical setup is constructed before the process begins:

(A) Two solutions having different concentrations of the same solute are taken: You must first have the two components (e.g., saltwater and pure water) ready for the process.

(C) A semipermeable membrane is inserted between the two solutions: The physical barrier that allows only solvent molecules to pass must be in place to separate the two concentrations.

(B) Very high external pressure is applied on the high concentration side: Once the setup is ready, you must apply a pressure greater than the osmotic pressure ($\pi$) to the concentrated side to "reverse" the natural flow.

(D) Solvent flows from the high concentration side to the low concentration one: This is the result of the applied pressure—pure solvent is forced through the membrane out of the concentrated solution.

Comparison with Normal Osmosis

• Normal Osmosis: Solvent flows spontaneously from Low $\rightarrow$ High concentration.
• Reverse Osmosis: External pressure forces solvent from High $\rightarrow$ Low concentration.