Concept: Relative density is a dimensionless ratio because it compares two similar quantities, so it has no S.I unit.
Explanation: Relative density is the ratio of the density of a substance to the density of water at
4∘C.
Both densities are measured in the same unit, so the units cancel out.
It can also be expressed as the ratio of the weight of a substance to the weight of an equal volume of water:
RD=w1−w2w1 Since the numerator and denominator are both weights, the units cancel.
Therefore, relative density is a pure number with no S.I unit.
Answer: Relative density has no S.I unit — option D.