Correct Answer: Lactometer - Specific gravity of liquids

Solution : The correct option is the Lactometer - specific gravity of liquids .

A hydrometer or lactometer is a device that uses the concept of buoyancy to measure the density or relative density of liquids. Typically, they are graduated and calibrated using one or more scales, like specific gravity. A lactometer measures the specific gravity of milk, not liquids in general. It gauges milk density to assess its composition. Specific gravity is the ratio of a substance's density to the density of a reference substance, usually water. The lactometer is specific to assessing milk density, not that of all liquids.