What is the standard unit for molality?

• A. mol/kg
• B. mol/L
• C. g/L
• D. mol/m^3

Answer: (A)

Molality is defined as the number of moles of solute per kilogram of solvent, so its standard unit is mol/kg. This unit reflects concentration based on mass, not volume, which is why it stays essentially constant with temperature changes (mass is conserved even when liquids expand or contract). In contrast, molarity uses liters of solution (mol/L), which varies with temperature due to volume expansion or contraction. The other options describe either mass per volume or volume-based concentration, not the solute-per-mass framework of molality, so mol/kg is the correct standard unit.