Question:

On charging the lead storage battery, the oxidation state of lead changes from $\mathrm{x}_{1}$ to $\mathrm{y}_{1}$ at the anode and from $\mathrm{x}_{2}$ to $\mathrm{y}_{2}$ at the cathode. The values of $\mathrm{x}_{1}, \mathrm{y}_{1}, \mathrm{x}_{2}, \mathrm{y}_{2}$ are respectively:

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The oxidation states change during the charging of a lead-acid battery.

Updated On: Oct 31, 2025

$+4,+2,0,+2$
$+2,0,+2,+4$
$0,+2,+4,+2$
$+2,0,0,+4$

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The Correct Option is B

Approach Solution - 1

To solve this question, we need to understand the oxidation states involved in the charging process of a lead storage battery. Let's break down the process at both the anode and cathode and calculate the changes in oxidation states:

Anode Reaction:

During the charging of a lead-acid battery, the lead sulfate ($PbSO_4$) at the anode is converted back to lead ($Pb$).
In the discharged state, the oxidation state of lead in $PbSO_4$ is +2.
When $PbSO_4$ is converted to lead ($Pb$), which is elemental, the oxidation state becomes 0.
Thus, the change in oxidation state at the anode during charging is from +2 to 0.

Cathode Reaction:

At the cathode, lead dioxide ($PbO_2$) is converted back to lead sulfate ($PbSO_4$).
In the discharged state, the oxidation state of lead in $PbO_2$ is +4.
When it converts to $PbSO_4$, the oxidation state of lead becomes +2.
Thus, the change in oxidation state at the cathode during charging is from +4 to +2.

Therefore, the correct values for the oxidation state changes are:

Anode: $+2 \rightarrow 0$
Cathode: $+4 \rightarrow +2$

Thus, the correct option for the values of $x_1, y_1, x_2, y_2$ is:

$+2, 0, +2, +4$

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Approach Solution -2

1. Anode reaction: - $\mathrm{PbSO}_{4}$ is reduced to $\mathrm{Pb}$. - $\mathrm{Pb}^{2+} \rightarrow \mathrm{Pb}^{0}$ - $\mathrm{x}_{1} = +2$, $\mathrm{y}_{1} = 0$
2. Cathode reaction: - $\mathrm{PbSO}_{4}$ is oxidized to $\mathrm{PbO}_{2}$. - $\mathrm{Pb}^{2+} \rightarrow \mathrm{Pb}^{4+}$ - $\mathrm{x}_{2} = +2$, $\mathrm{y}_{2} = +4$
Therefore, the correct answer is (2) $+2,0,+2,+4$.

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