Given below are two statements : one is labelled as Assertion and the other is labelled as Reason. Assertion: At 10 ° C , the density of a 5 M solution of KCl [atomic masses of K & Cl are 39 & 35 . 5 g mol - 1 respectively], is ' x ' gml - 1 . The solution is cooled to - 21 ° C . The molality of the solution will remain unchanged. Reason: The molality of a solution does not change with temperature as mass remains una

Step-by-step solution

The freezing point depression, ΔT f is equal to the freezing point of the solvent minus the freezing point of the solution. It is also proportional to the molal concentration of the solute. Δ T f = K f m Where K f , the freezing point depression constant, depends only on the solvent. Molality is moles of solute per kg of solvent. So, the concentration of solvent is expressed in terms of mass, and the mass of a substance is not affected by the change in temperature. Hence, molality is independent of temperature.