State the law which is used to construct a hydrometer?

. The construction of a hydrometer is based on the Law of Archimedes, from which it follows that the weight of a liquid that is displaced by a suspended substance (in this case, a hydrometer) is equal to the weight of the suspended substance. The density of the fluid under investigation can be determined by the depth of the hydrometer’s immersion in the fluid (the volume of liquid displaced by it) and the weight of the hydrometer. In practice hydrometers are of two types: constant-weight hydrometers (most widely used) and constant-volume hydrometers.

Explanation:

hope this is correct

4d^55s^1 ( third choice)