For a lead storage battery, which of the following statements are correct?

ADuring discharge both the anode and the cathode get coated with $PbSO X_{4}$
BDuring discharge the concentration of $H X_{2} SO X_{4}$ increases
CTwo moles of $H X_{2} SO X_{4}$ are consumed for every two moles of electrons passed
DDuring charging, $PbSO X_{4}$ on the positive plate is reduced to metallic lead

Answer: A, C

Discharge: anode

Pb + SO X_{4} X^{2 -} PbSO X_{4} + 2 e X^{-}

, cathode

PbO X_{2} + 4 H X^{+} + SO X_{4} X^{2 -} + 2 e X^{-} PbSO X_{4} + 2 H X_{2} O

; overall

Pb + PbO X_{2} + 2 H X_{2} SO X_{4} 2 PbSO X_{4} + 2 H X_{2} O

. Both plates become

PbSO X_{4}

and

2 mol

H X_{2} SO X_{4}

are used per

2 mol

electrons, so (A) and (C) are correct, while the acid concentration decreases, so (B) is wrong. On charging the reactions reverse:

PbSO X_{4}

on the positive plate is oxidised to

PbO X_{2}

and that on the negative plate is reduced to

Pb

, so (D) is wrong.