What is the S.I. unit of relative density?

No units

The unit of relative density is dimensionless, meaning it has no units. To understand this, we first need to comprehend the concept of relative density.

Relative Density (RD) is defined as the ratio of the density of a substance to the density of water at a specific temperature (usually at 4°C where water has its maximum density). Mathematically, it can be expressed as:

RD = (Density of substance) / (Density of water)

Since density is the mass per unit volume, and both the substance and water are measured in the same units (e.g., kg/m³), the units cancel out in the ratio. This leads to the conclusion that relative density is a dimensionless quantity and therefore has no units.

Therefore, the correct answer is: a) No units.