Answer: An acid is a substance that donates a proton and produces a conjugate base.
Explanation:
According to Bronsted-Lowry theory, an acid is a substance that donates a proton and produces a conjugate base while a base is a molecule or ion which accepts the proton.
An example of Bronsted-Lowry acid and base is Ethanoic acid, CH3COOH and hydroxide ion, OH- respectively as shown in the reaction below
CH3COOH(aq) + OH-(aq) <---> CH3COO-(aq) + H2O(l)
Thus, ethanoic acid acts as an acid by donating a proton to the hydroxide ion which accepts it, thus producing ethanoate ion, CH3COO- as a conjugate base.
