Which pair of chemicals does NOT represent an acid/base conjugate pair?

Which pair of chemicals does NOT represent an acid/base conjugate pair?
  
a. Acetic acid and the acetate ion
   
b. Hydronium ion and hydroxide ion
   
c. Hydrogen sulfate ion and sulfate ion
   
d. Hydrochloric acid and the chloride ion

Roger the Mole2021-04-07T23:58:06Z

b. Hydronium ion and hydroxide ion