Which one of the following pairs is not a conjugate acid-base pair?

Question

Quizplus · Accepted Answer

All other pairs consist of a protonated species (having an additional H+ ion) and its corresponding deprotonated species (lost H+ ion) and are therefore conjugate acid-base pairs. However, in pair E (HCl/H⁺), HCl is a strong acid and dissociates completely in water, while H⁺ is a weak base and does not accept protons from HCl. Therefore, they are not a conjugate acid-base pair.

Which One of the Following Pairs Is Not a Conjugate