Regarding the operating principle of a reverse-osmosis type freshwater generator, what statement is true?

Correct Answer: Option D — External pressure is applied to the side of strong concentration forcing freshwater through the semi-permeable membrane to the side of weak concentration.

Reverse osmosis relies on applying external pressure to the concentrated solution side that exceeds the natural osmotic pressure. This force drives the solvent (freshwater) through the semi-permeable membrane toward the side of lower concentration, effectively separating the pure water from the dissolved salts and impurities in the feed.