The correct answer is: D. Sulphuric acid is consumed.
When a lead storage battery is discharged, the following reaction occurs:
$$Pb(s) + PbO_2(s) + 2H_2SO_4(aq) \to 2PbSO_4(s) + 2H_2O(l)$$
In this reaction, lead and lead dioxide are consumed, and sulfuric acid is consumed. The lead sulfate formed is a solid, and it coats the plates of the battery. This can reduce the capacity of the battery to store charge.
The other options are incorrect. Option A is incorrect because sulfur dioxide is not produced during the discharge of a lead storage battery. Option B is incorrect because lead sulfate is formed, not consumed. Option C is incorrect because lead is formed, not consumed.
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