In a chemical reaction, atoms are rearranged to form new substances. This happens predictably. The same reactants will form the same products no matter when or where the reaction takes place. For example, in a lab, you could combine iron and oxygen. The product will be the same iron oxide that forms on a rusty iron nail. Those are the same reactions. Similarly, if you've studied acids and bases, you probably know the products of a neutralization reaction. Acids and bases will combine in a chemical reaction to produce a salt and water.
Based on the passage, rust will form on an iron nail when what has occurred?
