Question

Relative density of mercury is:
a. 1.356
b. 13.56
c. 135.6
d. None of the above

Answer 1

Hint: We will start by defining the relative density or specific gravity and then we will find the density of mercury and water at standard temperature and pressure. Whose ratio will give us the relative density of mercury.

Complete step-by-step answer:
Relative density or specific gravity of a liquid or solid sample is given by the ratio of density of that sample to the density of water and that is why it is a dimensionless quantity.
Mathematically, relative density of a sample $\rho_{sample}=\dfrac{d_{sample}}{d_{{H}_{2}O}}$.
Water has been taken as the usual standard for determining the relative density of a solid or liquid. The density of water at $4^{\circ}C$ and one atmospheric pressure is considered as the standard and its density at that temperature and pressure is 1 kg per litre. And the density of mercury is 13.56 kg per litre.
Therefore, relative density of mercury, $\rho_{mercury}=\dfrac{d_{mercury}}{d_{{H}_{2}O}}=\dfrac{13.56}{1}$
Thus, $\rho_{mercury}=13.56$

Hence, option b is the correct answer.

Additional information:
Relative densities of gases are generally found by comparing the density of sample gas with the density of air whose value is 1.29 grams per litre under standard conditions of 273K temperature and one atmospheric pressure.
There are many real-life applications of relative density like it is the main logic behind buoyancy. Gemologists use relative density to distinguish different gems. It is also used by chemists to check the concentration of solutions and progress of reactions. Many ore-gangue separation methods also utilize the concept of relative density.

Note: In the case of many solids and liquids, most of the time their density is similar to the specific gravity. But we should also see that the conditions at which the density of the sample is measured should coincide with the conditions of that of water.