Question

The density of alcohol is $800kg/m^3$. Its relative density is:
A) 0.08
B) 0.8
C) 8
D) 80

Answer 1

Hint: Relative density of a substance is ratio of density of substance to the density of water (for liquids and solids only). Density of alcohol is given and we know that the density of water under standard conditions is $1000kg/m^3$. To find relative density divide density of substance with density of water.

Complete step by step answer:
Given, the density of alcohol is $800kg/m^3$ and we have to find relative density.
Relative density is ratio of a substance is ratio of density of substance to density of standard substance which is either air (for gaseous substance) or water (for liquid and solid substance).
Here alcohol is liquid then we use water to find relative density.
We know that the density of water is $1000kg/m^3$ under standard conditions. Density of water is different at different temperatures and pressures.
Relative density of alcohol is equal to division of density of alcohol by density of water.
$$D_{\text{Relative}}={\displaystyle \frac{\text{Density of alcohol}}{\text{Density of water}}}={\displaystyle \frac{800}{1000}}=0.8$$

Then the relative density of alcohol is 0.8 and the correct answer is option B .

Note:
We know that with change in temperature of a substance, volume of substance changes and density also. Then all the calculations are done for standard temperature and pressure conditions. If there is change in temperature or pressure of substance then relative density also changed. Also, in case of gases we use density of air to find relative density.