Concept:Adding a non-volatile solute like sodium chloride alters the boiling and freezing points of the solvent water.
Explanation:When
NaCl dissolves in water, it dissociates into ions, increasing the number of solute particles in the solution.
According to colligative properties, the vapour pressure of the solution decreases.
A lower vapour pressure means the solution must be heated to a higher temperature to boil, so the boiling point increases.
At the same time, the dissolved particles interfere with the formation of solid ice crystals, so the freezing point decreases.
Thus, the solution experiences freezing point depression and boiling point elevation.
Answer:D. decrease in freezing point and increase in the boiling point.