What is osmotic pressure a measure of?

Osmotic pressure is defined as the pressure required to prevent the flow of a solvent into a solution through a semipermeable membrane. This phenomenon occurs when a solvent moves from an area of lower solute concentration to an area of higher solute concentration, a process known as osmosis. The greater the concentration of solute in the solution, the higher the tendency for solvent molecules to move into that solution, thereby increasing the osmotic pressure. Thus, osmotic pressure effectively quantifies this tendency of solvent molecules to move, making option B the correct choice.

The other options focus on different physical properties or processes. The energy required to freeze a solvent relates more to the freezing point and enthalpy changes rather than osmotic pressure. The boiling point concerns the temperature at which a solvent changes from a liquid to a gas, which is unrelated to osmotic behavior. Finally, the speed of diffusion pertains to the rate at which molecules spread out due to concentration gradients, rather than the specific process of solvent movement governed by osmotic pressure.