Question

Why is the density of ice is lower than that of water?
A. volume of ice is more than water.
B. volume of water is more than ice
C. weight of ice.
D. none of the above

Answer 1

Density is the qualitative measure of relative "heaviness" of an object at constant volume.
It is also defined as mass per unit volume.
$Density = \frac{{Mass}}{{Volume}}$

Complete step by step answer: As we know, normally in most compounds density is inversely proportional to temperature. As the temperature increases, density becomes lower and vice-versa. But in the case of water: The maximum density of water is at $4^{o}$. Below this temperature the density of water decreases. This is known as "anomalous behaviour of water". This anomalous behaviour is accounted for in water due to extensive H- bonding present in it.
In ice, each molecule of Hydrogen is bonded with four other molecules which create a mesh like structure. The air traps in the mesh and aids in lowering the density of ice. Moreover due to the hexagonal crystal structure formation in ice, the volume of the molecule increases. Since, volume is inversely proportional to Density, thus the density of ice ultimately decreases and becomes less than water. The molecules in the water are more closely packed and therefore make it denser.
So, the correct answer is “Option A”.

Additional Information: The units of density are:
$Density = \frac{{Mass}}{{Volume}} = \frac{{Kg}}{{{m^3}}} = Kg{m^{ - 3}}$
Thus, the S.I units of density is Kilogram per cubic meter.

Note:
- Density of water is $997Kg/{m^3}$ and the density of ice is about $920Kg/{m^3}$.
- The $C.G.S$ units of Density is $gc{m^{ - 3}}$ i.e. gram per cubic centimeter.