Which of the following best describes a hydrometer?

• A. An apparatus for measuring the temperature of gases.
• B. An instrument used to measure the density of liquids.
• C. A tool used to determine the pH of a solution.
• D. A device for measuring atmospheric pressure.

Answer: (B)

Verified step by step guidance

1. Understand that a hydrometer is a scientific instrument used in chemistry and physics to measure a specific property of liquids.
2. Recall that the primary function of a hydrometer is to measure the density or specific gravity of a liquid, which is the ratio of the density of the liquid to the density of water.
3. Recognize that the other options describe different instruments: a thermometer measures temperature, a pH meter measures acidity/basicity, and a barometer measures atmospheric pressure.
4. Conclude that the best description of a hydrometer is 'an instrument used to measure the density of liquids.'
5. Note that hydrometers typically consist of a weighted, sealed glass tube that floats in the liquid, and the level to which it sinks corresponds to the liquid's density.