Lactometers and hydrometers work on _______________________.

 The Archimedes principle states that an upward force, known as buoyant force, acts on a partially or completely submerged mass in a fluid. This force has the same magnitude as the weight of the fluid displaced by the body.

Lactometer: A lactometer is a device that measures the purity of milk.

It operates according to Archimedes' principle.

The vertical force experienced by a solid suspended in a fluid is equal to the weight of the fluid displaced.

Hydrometer: It works on the same Archimedes principle as the thermometer.

It is used to determine the fluid's (specific) density.

The hydrometer sinks further as the density of the fluid decreases.

Option C is the correct response.