Define and state density and relative density.
Density: The density of a substance is defined as mass of the substance per unit volume i.e.
Density = Mass / Volume . The SI unit of density is kg/m3
Relative Density: The Relative Density of a substance is the ratio of its density to that of water. i.e.
Relative Density = Density of substance / Density of water. Relative Density is unitless.