Final answer:
The vapor pressure of a solution is directly affected by the number of solute molecules present.
Step-by-step explanation:
The vapor pressure of a solution is indeed directly affected by the number of solute molecules present. When a solute is dissolved in a solvent, it occupies surface sites at the solution's surface. The more solute molecules present, the more surface sites occupied, resulting in a decrease in vapor pressure. This relationship holds true as long as the solute and solvent have similar particle sizes and probabilities of being at the surface.