Final answer:
The factor that would reduce the yield of a reaction is when the reaction is reversible as it allows products to convert back into reactants.
Step-by-step explanation:
The factor that would reduce the yield of a reaction is C. the reaction may be reversible. Reversible reactions mean the products can react to form reactants again, thus reducing the amount of product obtained from a reaction. This reversibility can be represented by a double arrow in a chemical equation, signaling that both the forward and reverse reactions occur simultaneously. In contrast, exothermic reactions (A. The reaction produces a large quantity of heat), fast reactions (B. The reaction occurs very quickly), and reactions where products are more stable than reactants (D. The products are more stable than the reactants) can often contribute to higher yields, under the right conditions.