Question

Assertion: Increasing pressure on pure water decreases its freezing point.
Reason: Density of water is maximum at ${{4}^{o}}C$
(A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
(B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
(C) Assertion is correct but Reason is incorrect
(D) Assertion is incorrect but Assertion is incorrect

Answer 1

Hint: The freezing point of substance is a dynamic equilibrium between the solid phase and liquid phase. It is defined as the temperature at which the vapour pressure of the substance in the liquid phase is equal to the vapour pressure in the solid phase. There are more properties of the solution which depends on the vapour pressure of the solvent.

Complete step by step answer:
Given Assertion statement: Increasing pressure on pure water decreases its freezing point
We know that with increasing atmospheric pressure, the freezing point of water slightly decreases. Because of increasing the pressure, which prevents water molecules properly arranging them. If water freezes, the mean forms a crystalline solid phase with a proper arrangement. Now what happens when pressure increases water molecules cannot be properly arranged, so water cannot freezes at the freezing point at 273K. That means water freezes at below 273K.
Hence, the given statement “Increasing pressure on pure water decreases its freezing point” is true.
Reason: Density of water is maximum at ${{4}^{o}}C$.
The maximum density of water at ${{4}^{o}}C$, because the temperature of water decreases, the water molecules slow down, and coming close together, density increases.
Both Assertion and Reason statements are true, but the Reason statement is not the correct explanation for Assertion.
Hence, option B is correct.

Note: When ice melts to liquid, density will increase as the structure collapses. Increasing temperature after freezing molecules moves faster than density decreases. At ${{4}^{o}}C$, the water clusters are forming which makes the molecules apart, hence the density starts decreasing. So, the Density of water is maximum at ${{4}^{o}}C$.