Question

The boiling and freezingvpoint of water on mixing an adible salt

Answer 1

the salt increase the boiling point and decrease the freezing point of water , it happens because these boiling point elevation and freezing point depression.  Basically for boiling point elevation the solvent (water) and solute (salt) have this interaction.

The freezing point depression can also be explained in terms of vapor pressure. Addition of solute to a solvent will essentially dilute the solvent molecules, and according to Raoult's law this leads to a decrease in vapor pressure. Considering the fact that the vapor pressure of the solid and liquid forms must be the same at freezing point (or else the system would not be at equilibrium), the lowering of the vapor pressure leads to the lowering of the temperature at which the vapor pressures of the liquid and frozen forms of the solution will be equal.

When a solute is added to the solvent, some of the solute molecules occupy the space near the surface of the liquid, as shown in the figure below. When a solute is dissolved in a solvent, the number of solvent molecules near the surface decreases, and the vapor pressure of the solvent decreases.