Question

Density of water at ${{4}^{{}^\circ }}C$is
$\text{A}\text{. minimum}$
$\text{B}\text{. maximum}$
$\text{C}\text{. 1}{{\text{0}}^{3}}kg/{{m}^{3}}$
$\text{D}\text{. }1kg/{{m}^{3}}$

Answer 1

Hint: Density of any material is the mass per unit volume of that substance. Density of the substance depends on interatomic spacing. More the interatomic space, lesser is the density of the material.
Although other materials expand on heating water as an exception contracts on heating between ${{0}^{{}^\circ }}C$and ${{4}^{{}^\circ }}C$.

Complete step-by-step answer:
The density of a material is the mass of the substance present in its unit volume. It is usually denoted by $\rho$ and has SI unit $kg\text{ }{{m}^{-3}}$
$\rho =\dfrac{m}{V}$
Where
$m=\text{ mass of the substance}$
$V=\text{ volume of the substance}$
Density of a substance varies with pressure and temperature.
As pressure on substance increases, intermolecular spacing decreases and as a consequence its density increases.
Usually with increase in temperature, substance expands and as a result volume of the substance increases. As a consequence density of material decreases. But there are some exceptions.
Water contracts on heating between ${{0}^{{}^\circ }}C$and ${{4}^{{}^\circ }}C$. When water is cooled, its volume decreases continuously until its temperature reaches ${{4}^{{}^\circ }}C$ and after that its volume increases. As a result, its density increases until ${{4}^{{}^\circ }}C$temperature on cooling. Hence we can conclude that water has maximum density at temperature${{4}^{{}^\circ }}C$.
The density of water at ${{4}^{{}^\circ }}C$is $1g\text{ }m{{L}^{-1}}$ or ${{10}^{3}}kg\text{ }{{m}^{-3}}$.

So, the correct answer is “Option B and C”.

Additional Information: This property of water is very much important for the environment as water bodies like lakes and ponds, freeze at the top first. If water didn't have this property, lakes and ponds would freeze from rock bottom up. This could have destroyed much of aquatic life.

Note: The temperature dependence of density of water is not linear. Density of water when not given in the problem is to be assumed as $1g\text{ }m{{L}^{-1}}$.
Students need to remember the density variation of water as it is an exceptional case. Otherwise students may get confused and can answer it as in usual material and attempt incorrect answers.