🔍 Key Concepts

• Hydrometer as an instrument that floats higher or lower depending on liquid density • Relationship between density and specific gravity of a liquid • Common engine room use: checking condition of lead‑acid batteries

💭 Think About

• Which choice involves comparing how heavy a liquid is compared to water, rather than pressure, quantity, or power? • In an engine room or maintenance context, when would you need an instrument that floats in a liquid and has a scale on its stem? • Think about which option is about the property of the liquid itself rather than about the system the liquid is used in.

✅ Before You Answer

• Does the instrument directly measure density/specific gravity of a liquid, or is it about pumps/pipes/tank volume? • Which answer mentions a property of a liquid rather than of the system (pump power, line pressure, tank capacity)? • Picture using a hydrometer in a small sample container — which of these tasks is done with a small sample, not a whole system?