Automotive batteries — electrolyte identification In conventional lead–acid starting batteries used in automobiles, the electrolyte is a water solution of which acid?

Introduction / Context:
Lead–acid batteries dominate automotive cranking applications because of low cost and high surge current capability. The electrolyte chemistry determines performance, safety, and service procedures. Correctly identifying the acid ensures proper handling and maintenance.

Given Data / Assumptions:

• Typical 12 V flooded or absorbent glass mat lead–acid battery.
• Electrodes are lead dioxide (positive) and sponge lead (negative).
• Electrolyte is an aqueous acid solution.

Concept / Approach:
Lead–acid cells use sulphuric acid in water. During discharge, lead and lead dioxide react with sulphuric acid to form lead sulfate and water, lowering electrolyte specific gravity. During charge, the reaction reverses. Other strong acids listed are not used and would severely attack materials or be unsafe in this context.

Step-by-Step Solution:
Identify battery type: lead–acid.Recall chemistry: sulphuric acid electrolyte participates in reversible reactions.Select sulphuric acid as the correct electrolyte.

Verification / Alternative check:
Service tools such as hydrometers measure electrolyte specific gravity, a direct indicator of sulphuric acid concentration and state of charge.

Why Other Options Are Wrong:
Hydrochloric, nitric, and hydrofluoric acids are incompatible and unsafe for this electrochemical system, offering no performance advantage and significant hazards.

Common Pitfalls:
Adding acid to raise specific gravity as a substitute for charging; correct practice is to add distilled water to restore level and charge the battery properly.

Final Answer:
sulphuric acid