What is typically used as the electrolyte solution in a lead-acid battery?

In a lead-acid battery, the typical electrolyte solution is indeed a mixture of water and sulfuric acid. This combination creates a highly conductive solution that facilitates the electrochemical reactions necessary for the battery's operation. During discharge, lead dioxide (PbO2) and sponge lead (Pb) react with the sulfuric acid to produce lead sulfate (PbSO4) and water, while during charging, this process is reversed.

Sulfuric acid serves as an effective medium for the transfer of ions between the positive plate (lead dioxide) and the negative plate (sponge lead). The concentration of sulfuric acid affects the battery's voltage and overall performance, making this specific mixture crucial for efficient charging and discharging cycles in lead-acid batteries.

The other options presented do not represent valid components of a lead-acid battery's electrolyte. Hydroxide ions are involved in alkaline batteries rather than lead-acid batteries, and cadmium is associated with nickel-cadmium (NiCd) batteries. Boric acid does not constitute a typical electrolyte in lead-acid battery systems. Thus, the use of a water and sulfuric acid mixture is fundamental to the chemistry and functionality of lead-acid batteries.