Lead–acid battery chemistry — composition of the positive plates In a standard lead–acid starter battery used in automobiles, what active material is on the positive plates?

Introduction / Context:
Understanding the electrochemistry of lead–acid batteries helps with diagnostics, charging, and maintenance. Identifying the correct active materials on positive and negative plates is fundamental.

Given Data / Assumptions:

• Conventional flooded lead–acid automotive battery.
• Normal charged condition.

Concept / Approach:
In the charged state, the positive plate's active material is lead dioxide (lead peroxide, PbO2), and the negative plate's active material is spongy lead (Pb). The electrolyte is sulphuric acid in water. During discharge, both plates trend toward lead sulphate (PbSO4).

Step-by-Step Solution:
Recall charged composition: positive = PbO2, negative = Pb, electrolyte = H2SO4.During discharge, chemical reactions form PbSO4 on both plates and reduce acid concentration.Thus, the correct positive-plate material in the charged state is lead peroxide (PbO2).

Verification / Alternative check:
Battery test charts and textbooks universally specify PbO2 for the positive plate in charged condition.

Why Other Options Are Wrong:

• Spongy lead (Pb): that is the negative plate in the charged state.
• Lead sulphate (PbSO4): appears on both plates when discharged.
• H2SO4: this is the electrolyte, not plate material.

Common Pitfalls:
Mixing up charged vs discharged states; remembering “peroxide is positive” helps.

Final Answer:
lead peroxide (PbO2)