The correct answer is: A. PbO2
During the idle period of the battery, strong electrolyte tends to change the active material of the cell into PbO2. This is because the strong electrolyte will react with the lead sulfate in the battery to form PbO2. PbO2 is a more stable material than lead sulfate, so it will tend to form on the surface of the lead plates in the battery. This can lead to a loss of capacity in the battery, as the PbO2 is not as effective at storing charge as lead sulfate.
Option B, PbSC4, is incorrect because it is not a stable material. It would decompose into PbO2 and sulfur.
Option C, PbO, is incorrect because it is not a stable material. It would decompose into Pb and oxygen.
Option D, Pb, is incorrect because it is the starting material for the formation of PbO2.