Which device listed among valve types is used to measure the density of liquids and is included in the valve types list?

• A. Electric valve
• B. Manual valve
• C. Hydrometer
• D. Three-way

Answer: (C)

Measuring liquid density relies on buoyancy principles. A hydrometer is designed to determine density (or specific gravity) by floating in the liquid; the float sinks until buoyancy balances weight, and the depth of immersion corresponds to the liquid’s density. The reading is taken from a scale on the stem at the liquid surface, so denser liquids cause the hydrometer to float higher and yield a higher density reading on the scale.

The other options are types of valves that control or direct flow, not instruments for measuring density. An electric valve and a manual valve regulate whether and how much fluid passes through, while a three-way valve redirects flow. They don’t provide density measurements, so the hydrometer is the correct device for measuring liquid density.