Salutations!
What is the definition of the word acid in this sentence: The acid in the lemon made my mouth pucker.
Sour would be the best definition of the word acid. As it says 'lemon'. Lemon is always sour. When you eat something sour, your mouth has some wrinkles across, which means pucker.
Thus, your answer is option C.
Hope I helped (:
Have a great day!
