Question

The density of water is maximum at?
A.${0^ \circ }C.$
B. ${4^ \circ }C.$
C.${25^ \circ }C.$
D. ${100^ \circ }C.$

Answer 1

We know that the density of any material is defined as the mass per unit volume and it is the measurement of the rigidity of the material.
${\text{Density = }}\dfrac{{{\text{Mass}}}}{{{\text{Volume}}}}$

Complete step by step answer:
Now we see what the density of water means is.
We can define the weight of water per its unit volume as the density of water and it depends on the temperature of the water.
We know that density and the volume of the material are inversely proportional to each other which means that as volume decreases the density increases.
Below ${0^ \circ }C$ water is in its solid form called ice. In its solid form water molecules are present in a crystal lattice which has a lot of space which increases the volume due to increased volume the density gets lower. Thus option (A) is incorrect.
At ${{\text{4}}^{\text{o}}}{\text{C}}$ the structure of the ice starts to break and the water molecules move faster closing the empty voids due to that volume of water decreases which increase the density. Hence option (B) is correct.
If the temperature increases above ${{\text{4}}^{\text{o}}}{\text{C}}$ motion of water molecule increases and the extra space are needed by the molecules so they start to move away from each other which again increase the volume thereafter the density of water decreases. Hence option (C) and (D) are incorrect.
So the correct answer is option (B).

Note:
We must know that the ice floats in water because water has maximum density at ${{\text{4}}^{\text{o}}}{\text{C}}$ and at ${0^ \circ }C$ the density of ice is less than liquid. The density of water at room temperature is $997.77Kg/{m^3}.$