ANS:A - molal concentration

Molal concentration, often denoted as 𝑚m, is a measure of concentration used in chemistry. It represents the number of moles of solute dissolved in one kilogram of solvent. Mathematically, it is expressed as: 𝑚=𝑛solute𝑚solventm=msolvent​nsolute​​ Where:

• 𝑚m is the molality (molal concentration),
• 𝑛solutensolute​ is the number of moles of solute,
• 𝑚solventmsolvent​ is the mass of the solvent in kilograms.

Unlike molarity, which is based on the volume of the solvent, molality is based on the mass of the solvent. This makes molality particularly useful in situations where the temperature changes significantly, as it remains constant regardless of temperature changes. This is important in certain applications, such as colligative properties like boiling point elevation and freezing point depression, which are dependent on the number of solute particles rather than the volume of the solution.