Final answer:
Osmosis is the movement of water across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration, described by option c.
Step-by-step explanation:
Osmosis is the diffusion of water molecules across a selectively permeable membrane. When two solutions of different concentrations are separated by such a membrane, water moves from the area of higher water concentration (or lesser solute concentration) to an area of lower water concentration (or greater solute concentration). This movement aims to equalize solute concentrations on both sides of the membrane, thus achieving an isotonic state.
The correct answer to the student's question is c. The movement of water from an area of greater concentration to one of lesser concentration. This describes osmosis, where the water moves across a semipermeable membrane to balance the concentration of solutes, which cannot cross the membrane.