Which of the following is a conjugate acid-base pair?

Question

Which of the following is a conjugate acid-base pair?

a)NH2^- and NH4^+

b)none of these

c)all of these

d) Naf and F^-

e)H2O and O^2-

Answer 1

A conjugate acid-base pair are necessarily two molecules that look very similar, but with one key difference: the acid in the pair will have an additional H⁺compared to the base, i.e. the base will be missing an H and have a charge that is one unit lower than the acid. For example, NH₃ and NH₄⁺ are a conjugate acid-base pair, with NH₄⁺ being the acid, and NH₃ being the base (one less H, one unit lower charge).

From the options shown, NH₂^- and NH₄⁺ don't meet this condition, and neither do H₂O and O^2-. As far as NaF and F^-, these are essentially the same thing, because the ionic compound NaF includes the F^- ion.