Question

What is the reason to mention 4°C to define relative density?
​

Answer 1

Answer:

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 for liquids is nearly always measured with respect to water at its densest (at 4 °C or 39.2 °F); for gases, the reference is air at room temperature (20 °C or 68 °F). The term "relative density" is often preferred in scientific usage.

Answer 2

At 4 degree celcius, wtaer has the maximum density and hence we mention 4 degree celcius in relative density.