Question

expain relative density and what is the unit of relative density

Answer 1

Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water. ... For example, an ice cube, with a relative density of about 0.91, will float.

Answer 2

relative density is the ratio of density with respect to water at 4 degree Celsius
As this is a ratio so no SI UNIT