The optimal ratio of acetic anhydride to salicylic acid for the highest yield of acetylsalicylic acid aspirin during the synthesis process is 1:1, based on their stoichiometry. The balanced chemical equation for the synthesis of acetylsalicylic acid is:C7H6O3 salicylic acid + C4H6O3 acetic anhydride C9H8O4 acetylsalicylic acid + C2H4O2 acetic acid As per the balanced equation, one mole of salicylic acid reacts with one mole of acetic anhydride to produce one mole of acetylsalicylic acid. Therefore, the optimal molar ratio is 1:1. To achieve the highest yield, it is essential to use equimolar amounts of both reactants.