International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

The balanced equation for the reaction between hydrochloric acid (HCl) and manganese dioxide (MnO₂) is indeed represented by the equation that shows four molecules of HCl reacting with one molecule of MnO₂ to produce one molecule of manganese(II) chloride (MnCl₂), one molecule of water (H₂O), and one molecule of chlorine gas (Cl₂).

In this reaction, HCl acts as the acid, providing protons (H⁺) which react with moisture from MnO₂ to release Cl₂ gas. The stoichiometry of the reaction indicates that four HCl molecules are required to provide enough chloride ions for the formation of one manganese(II) chloride, along with the release of chlorine gas.

This is essential to balance the chlorine atoms on both sides of the equation, as there are four Cl atoms in the reactants (from 4 HCl) compared to one in MnCl₂ and one in Cl₂, summing to a total of four Cl atoms in the products. Thus, the balanced equation reflects the conservation of mass and charge throughout the reaction process.

The correct answer ensures that all atoms of each element are accounted for in both reactants and products, thus elegantly fulfilling the requirements