Which of the following affects the osmolality of a solution?

The osmolality of a solution is fundamentally influenced by the number of solute particles present in that solution. Osmolality is a measure of how many particles are dissolved in a given quantity of solvent, typically expressed in osmoles per kilogram of solvent. This means that as the concentration of solute particles increases, the osmolality of the solution also increases.

Factors such as temperature, color, and viscosity do not directly change the particle count in a solution, and therefore they do not impact osmolality in the same significant way that particle number does. Temperature can influence the behavior of solute particles and the solvent's physical state but does not alter the actual quantity of dissolved particles. Color is a property related to the presence of specific substances or concentrations, but it does not inherently provide information about particle concentration affecting osmolality. Viscosity pertains to the thickness of a fluid and can be influenced by particle interactions but again does not directly change the number of particles in solution.

Thus, understanding that osmolality is directly related to the number of dissolved particles clarifies why this aspect is the determining factor for osmolality changes in a solution.