Answer:
The corect answer is some of the reactants were spilled.
Step-by-step explanation:
Before the initiation of the reaction the total mass of both reactants is 15.0 grams and after the reaction the net mass of product is grams 12.4grams.
This happens because during the reaction some reactant molecules were spilled which ultimately leads to decrease the mass of the reactant molecule.
The decrease in the amount of the reactant equals with amount of product formed.