Which is the correctly balanced equation for the reaction of rust, Fe2O3, and hydrochloric acid, HCl?

Start with Fe2O3 + HCl → FeCl3 + H2O. Put 2 before FeCl3 to match the 2 iron atoms, which requires 6 chlorine atoms, so put 6 before HCl. Those 6 hydrogen atoms form 3 H2O, matching the 3 oxygen atoms; therefore the correctly balanced equation is Fe2O3 + 6 HCl → 2 FeCl3 + 3 H2O, choice C.

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