Which set of equipment would be most useful to determine the density of a liquid?

The instrument used to measure the density of a liquid is a hydrometer. These are often made for specific purposes, because the density of a given liquid may not vary much. Milk hydrometers are used to estimate the creaminess of raw milk. A battery hydrometer is used on your car battery, for the density of the sulphuric acid varies with the amount of lead dissolved, which indicates the state to which the battery is charged.