A Bronsted-Lowry acid is a proton donor (usually hydrogen ion). And a Bronsted-Lowry base is a proton acceptor (usually hydrogen ion). Consider a chemical reaction between HCl and NaOH. We have the reaction HCl + NaOH à NaCl + H2O. The hydroxide ions in the NaOH are bases because they accept hydrogen ions from acids to form water. And an acid produces hydrogen ions in solution by giving a proton to the water molecule. Therefore, the answer is d. a Bronsted-Lowry base.