Final answer:
The chemical reaction in an automotive battery produces hydrogen gas, which is highly flammable and can form explosive mixtures with the air, making it a hazard during the battery recharging process.
Step-by-step explanation:
The explosive gas produced by the chemical reaction of the metal plates and sulfuric acid in an automotive battery is hydrogen gas. In a lead-acid battery, the interaction between lead, lead (IV) oxide, and sulfuric acid generates lead sulfate and water, along with the release of hydrogen gas. This reaction can be represented as follows: Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O. During the recharging process, the reverse reaction leads to the evolution of hydrogen and oxygen gases as per the reaction 2H2O(l) → 2H2(g) + O2(g). Because hydrogen gas is highly flammable and can form explosive mixtures with air, it is crucial that the recharging of lead-acid batteries is carefully monitored to avoid the risks associated with hydrogen gas accumulation.