Question

The freezing point of pure water is...
A. 100 degree centigrade
B. 50 degree centigrade
C. 20 degree centigrade
D. zero degree centigrade

Answer 1

Hint: In simple language we use freezing point to refer to the temperature at which a liquid turns into solid when cooled. Sometimes we also use the term to describe the process when liquid starts freezing.

Complete step by step solution:
Pure water means without impurities. The term freezing point is used to refer to the temperature where liquid converts into solid.
Water converts into ice at zero degree centigrade.
At sea boiling point of water is 100 degree centigrade.
If the impurities are present the freezing point of liquid decreases.
So, from above we can conclude that the freezing point of pure water is zero degree centigrade. Therefore, option D is correct.

Additional Information:
When the temperature of water molecules approaches 13 degree centigrade, the water molecules form tetrahedrons, with each molecule loosely bonding to four other molecules.
In this process of forming tetrahedron the density of the water molecules decreases, its heat capacity increases and its compressibility also increases.
This change in structure of water controls the rate at which ice forms.

Note: The freezing point of any substance depends upon the atmospheric pressure. Generally when the pressure is lower than 1 atmosphere the temperature at which a substance freezes decreases, but for water, a higher pressure gives a lower freezing point.