Which of the following would require the largest volume of 0.100 m sodium hydroxide solution for neutralization? :

(a) 20.0 ml of 0.0500 m nitric acid
(b) 15.0 ml of 0.0500 m hydrobromic acid
(c) 5.0 ml of 0.0100 m sulfuric acid
(d) 10.0 ml of 0.00500 m phosphoric acid

10.0 mL of 0.00500 M phosphoric acid

Explanation:

If we look at the Ka values of the acids, we will realize that phosphoric acid has a Ka of 7.1 * 10-3. It is the only acid in the list having acid dissociation constant less than 1. This means that it does not ionize easily in solution and a very large volume of base must be added to ensure that it reacts completely. Acids with Ka >1 are generally regarded as strong acids. All the acids listed have Ka>1 except phosphoric acid.

they are all solids.