Which of the following represents molality?

Molality is defined as the number of moles of solute per kilogram of solvent. This measurement focuses specifically on the solvent, rather than the total solution, which is crucial in situations where temperature and pressure may affect the solution's volume but not its mass.

When calculating molality, it is important to consider only the mass of the solvent (the component in which the solute is dissolved) rather than the volume of the solution. This is significant in scientific contexts where precise concentrations are needed, particularly in colligative properties such as boiling point elevation and freezing point depression.

The use of moles for solute and kilograms for solvent distinguishes molality from other concentration measures, such as molarity, which is based on the volume of the entire solution. This makes B the accurate definition of molality.