1.Normality :

Normality depends on the volume of the solution. Heating generally causes the volume to expand, thus changing the normality.

2. Molarity :

Molarity is defined as the number of moles of solute per liter of solution. Since the volume of the solution changes with temperature, molarity will also change upon heating.

3. Molality (m):

Molality is defined as the number of moles of solute per kilogram of solvent. Since the mass of the solvent does not change with temperature, the molality remains unchanged when a solution is heated.

4. Density:

Density is mass per unit volume. Heating generally causes the volume to expand (assuming constant mass), thereby reducing the density.

Given this analysis, the correct answer is: the molality of the solution