Which of the following is NOT a colligative property?

Colligative properties are properties of solutions that depend on the number of solute particles in a given amount of solvent, rather than the identity of the solute. Common examples of colligative properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

Density, on the other hand, is an intensive property that depends on the ratio of mass to volume of a substance and is influenced by the nature of the substances in question as well as temperature and pressure. While the presence of solute can impact the density of a solution, this effect is not classified as a colligative property because it does not solely rely on the number of solute particles.

In contrast, vapor pressure, boiling point, and freezing point all illustrate how the collective quantity of solute particles alters the properties of the solvent. For example, the addition of a non-volatile solute will lower the vapor pressure of the solvent, raise its boiling point, and lower its freezing point. Therefore, density does not fit the criteria for colligative properties, confirming it as the correct choice for the question.