Final answer:
Boiling point elevation and freezing point depression are colligative properties depending on the molality of a solution, leading to an increase in boiling point and decrease in freezing point when a solute is added. therefore, the correct option is A.
Step-by-step explanation:
Boiling point elevation and freezing point depression are colligative properties that describe how the presence of a solute affects the boiling point and freezing point of a solvent. When a non-volatile solute is added to a solvent, the boiling point of the solution increases, which is referred to as boiling point elevation. Conversely, the addition of a solute also causes the freezing point of the solution to decrease, known as freezing point depression. Both of these phenomena are proportional to the molality of the solution, which is the number of moles of solute per kilogram of solvent. The calculation for these colligative properties in Chemistry makes use of specific constants: the boiling point elevation constant (Kb) and the freezing point depression constant (Kf). These constants are characteristic of each solvent. For example, water has specific Kb and Kf values that affect how saltwater's boiling and freezing points differ from pure water. A 2% saltwater solution will boil around 102°C, which is a boiling point elevation of 2°C due to the dissolved salt. In practical applications, these properties are utilized for processes like lowering the freezing point of water on roads using salts like NaCl or CaCl2 to prevent ice formation.