Answer: The required mass of KNO₃ is, 
Explanation: Provided,
Molal-freezing-point-depression constant
for water = 
Amount of water = 275 mL
Molar mass of KNO₃ = 101.1 g/mole
First, we need to determine the mass of the water.

Density of water = 1.00 g/mL

Next, we will figure out the mass of KNO₃
Formula utilized:

where,
= change in freezing point
= freezing point of solution = 
= freezing point of water = 
i = Van't Hoff factor = 2 (for KNO₃ electrolyte)
= freezing point constant for water = 
m = molality
Substituting all known values into this equation yields


Consequently, the mass of KNO₃ that must be added is, 