Lead Acid Battery

Step 1: Components of a lead acid cell.
The active materials in a lead-acid cell include spongy lead (Pb) on the negative plate, lead peroxide (PbO₂) on the positive plate, and sulfuric acid (H₂SO₄) as the electrolyte.
Step 2: Conclusion.
Thus, all the given materials are part of a lead-acid cell, corresponding to option (D).

Step 1: Understanding hydrogen evolution in lead-acid cells.
In a lead-acid battery, hydrogen gas is liberated at the negative plate during the charging process, where reduction occurs.
Step 2: Conclusion.
Thus, hydrogen is liberated at the negative plate, which corresponds to option (B).

Step 1: Understanding the process of charging.
In a lead-acid battery, during the charging process, the lead sulfate formed on the plates during discharge is converted back into lead dioxide and lead, and sulfuric acid is regenerated in the electrolyte.
Step 2: Effect on electrolyte concentration.
As the battery charges, the concentration of sulfuric acid in the electrolyte increases, making it stronger.
Step 3: Conclusion.
Thus, during charging, the electrolyte becomes stronger, which corresponds to option (A).