Question

density and relative density ?

Answer 1

Density is defined as mass per volume. Density of a material is the amount of substance contained in unit volume of the material. 
Relative density is the ratio of density of a substance to the density of a reference material. Usually, the reference material is water. Relative density is also known as specific gravity.

Answer 2

Density:"It is defined as the mass per unit volume of the substance."

Density, row=m÷v

M=mass of substance

V=volume of substance

St unit is Kgm-3

Relative density:

"It is defined as as the ratio of density of substance to the density of water.

Relative density has no unit

Density of water is 1000 kgm-3.

I hope it helps......