The reverse osmosis occurs when

Pressure on solution side is larger than osmotic pressure

The correct answer is Option (1) → Pressure on solution side is larger than osmotic pressure

• Osmosis: Solvent (water) moves from pure solvent (or dilute solution) side to concentrated solution side when only a semipermeable membrane separates them.
• Osmotic pressure (π): The minimum external pressure that must be applied on the solution side to just stop osmosis.
• Reverse Osmosis: When we apply pressure greater than the osmotic pressure on the solution side, the flow of solvent reverses — water moves from the concentrated solution side to the pure solvent side.

Hence, reverse osmosis occurs when: Applied pressure > Osmotic pressure

So, the correct option is: Pressure on solution side is larger than osmotic pressure