Question

What is meant by relative density of a substance? what is its significance ? the relative density of mercury is 13.6 what is its density in si units?

Answer 1

relative density is the ratio of denisity of substance with respect to water.
it helps you to determine that the object will sink or float in water

Answer 2

the ratio of the density of a substance to the density of a standard, usually water for a liquid or solid, and air for a gas.