A stoichiometric mixture is one in which the reactants are:

• A. In the correct proportion for a complete reaction
• B. In excess of one another
• C. In equal molar amounts
• D. In random proportions

Answer: (A)

A stoichiometric mixture means the reactants are present in the exact mole ratio required by the balanced equation to allow the reaction to go to completion with no leftovers. That precise proportion comes from the stoichiometric coefficients, and when the mixture matches it, both reactants are consumed completely (assuming the reaction goes to completion). If there’s extra of one reactant, it’s in excess and not stoichiometric. If there’s less of one reactant, the other becomes the limiting reactant and the reaction can’t use all of it. Equal molar amounts could be correct only in cases where the balanced equation has equal coefficients; otherwise, it isn’t the general definition. Random proportions won’t guarantee a complete reaction.