What electrolyte is used in a lead-acid battery?

• A. Pure water
• B. Mixture of sulfuric acid and water
• C. Potassium hydroxide solution
• D. Sodium chloride solution

Answer: (B)

Lead-acid batteries rely on a sulfuric acid–water electrolyte. The sulfuric acid dissociates to provide ions that carry charge between the positive and negative plates, enabling the reversible chemical reactions that store and release electrical energy. The water portion acts as the solvent and helps manage electrolyte concentration. During discharge, lead sulfate forms on the plates and the acid becomes more dilute; during charging, the reactions are reversed and sulfuric acid is regenerated, restoring the electrolyte. Pure water wouldn’t supply enough ions to conduct electricity well, a potassium hydroxide solution would create a different alkaline chemistry, and a sodium chloride solution wouldn’t support the lead–sulfate reactions properly.