A safety precaution designed to prolong the life of a lead acid accumulator is

Analyze the question: You are asked which option is a safety precaution that helps a lead-acid accumulator (car battery) last longer.

Concept: A lead-acid accumulator has lead plates in dilute sulphuric acid (the electrolyte). While it discharges, the acid is used up and the specific gravity (relative density) of the electrolyte falls. While it charges, the specific gravity rises again. A fully charged cell reads about 1.25-1.28, and a discharged one falls to about 1.15 or lower. If the specific gravity is allowed to drop too low, lead sulphate hardens on the plates (sulphation), which permanently reduces capacity and shortens the battery's life. Checking it with a hydrometer and keeping it within the recommended range protects the battery.

Evaluate each option:

• A. Topping up with concentrated acid: Wrong. Only water (distilled water) is added to replace what evaporates. Adding concentrated acid makes the electrolyte too strong and damages the plates.
• B. Naked flame while charging: Wrong and dangerous. Charging releases hydrogen gas, which is explosive near a flame.
• C. Keeping the specific gravity of the electrolyte within the specified range: Correct. It prevents sulphation and over-concentration, so the battery lasts longer.
• D. Connecting wires directly across the terminals to test charge: Wrong. This short-circuits the battery, causing a very large current, heating, and damage. A hydrometer or voltmeter should be used instead.

Answer: C

Exam tip: Remember "water in, not acid; no flame, no shorting; check the hydrometer." Whenever a lead-acid question asks about care or maintenance, look for the option mentioning specific gravity, hydrometer, or distilled water.