Question

Density of water is maximum at
$
  {\text{A}}{\text{. 0}}^\circ {\text{C}} \\
  {\text{B}}{\text{. 4}}^\circ {\text{C}} \\
  {\text{C}}{\text{. 4K}} \\
  {\text{D}}{\text{. 100}}^\circ {\text{C}} \\
$

Answer 1

- Hint: Density of a material signifies the mass of the material per unit volume. Larger the interatomic space between molecules, lower is the density of the material. As we decrease the temperature of water, its density starts increasing.

Complete step-by-step answer:
The density of a material is equal to the mass contained in it per unit volume of that substance. The density of a material increases with decrease in temperature and decreases with increase in temperature.
The ice has water molecules arranged in a lattice structure. When water is cooled down to form ice, it is observed that the density of water keeps increasing but only up to 4$^\circ C$. The molecules come together and have highest density at 4$^\circ C$. When temperature is decreased below 4$^\circ C$, the ice starts to form up to 0$^\circ C$. The lattice structure of ice consists of water molecules which are widely separated from each other and the density observed is smaller compared to that observed at 4$^\circ C$.
In the reverse sense, when ice at 0$^\circ C$ starts melting, the molecules start filling up the empty spaces in the lattice. This process continues up to 4$^\circ C$ leading to highest density at this temperature. Beyond it the density further starts decreasing as the particles start pushing away from each other due to increase in kinetic energy with increase in temperature.
Hence, the correct answer is option B.
Note: The temperature of a material represents how much kinetic energy the molecules possess. Higher the temperature, higher is the kinetic energy and greater are the number of collisions between the molecules of that material.