Define the term ‘relative density. Write its SI unit. If the relative density of a substance is 0.8, is it heavier than or lighter than water?

Relative density:

1. Relative density is the ratio of the density of a substance to the density of water.
2. Relative density of water is 1.

SI Unit of relative density:

1. In the formula of relative density, the unit of numerator and denominator is the same and that is the unit of density.
2. So, relative density is a dimensionless quantity.

Relative density:

1. Relative density is the ratio of density of substance to the density of water.
2. Relative density of water is 1.

If the relative density of a substance is 0.8:

1. If relative density of a substance is 0.8 then it means it is of lesser density than water.
2. So, the substance with relative density 0.8, then it will be lighter than water and will float on water.

Hence, relative density is a dimensionless quantity and a substance having relative density less than one will be lighter than water.