Osmosis is best described as c) diffusion of water from a greater to a lesser water concentration across a selectively permeable membrane.
Osmosis specifically refers to the movement of water molecules through a selectively permeable membrane. This process involves water moving from an area where it is in greater concentration (more water, less solute) to an area where it is in lesser concentration (less water, more solute). This movement continues until equilibrium is reached, meaning that the concentration of water is equal on both sides of the membrane.
While option a mentions the movement of water into a solute, it lacks the critical aspect of concentration gradients and the role of a selectively permeable membrane. Option b does mention diffusion, but it does not include the selectivity of the membrane, which is essential to understanding how osmosis differs from simple diffusion.