What defines reverse osmosis in purification methods?

Reverse osmosis is defined by the application of pressure across a semipermeable membrane. This process allows for the selective passage of water molecules while preventing larger molecules and impurities from passing through. When pressure is applied to the solution side of the membrane, it forces water from a more concentrated solution to a less concentrated one, effectively purifying the water by removing various contaminants, salts, and particles.

The semipermeable membrane is crucial in this method, as it acts as a barrier that allows only specific molecules (like water) to pass through, which enhances the efficiency of purification. This mechanism is widely used in various applications, from desalinating seawater to purifying drinking water and treating wastewater.

In contrast, the other choices describe different methods of purification that do not involve the pressure-driven mechanism characteristic of reverse osmosis. For example, using heat to evaporate impurities pertains to distillation, filtering through resin beads typically relates to ion exchange processes, and using chemicals to bind impurities describes chemical treatment methods. Each of these methods has its own principles and applications but does not embody the concept of reverse osmosis.