chemistry question

It is easy.

for the equibrium: HF <==> H+(aq) + F-(aq)
Ka of HF = [H+][F-]/[HF]



Now you are looking for K of the combination of H+ with F-, which is the reverse of acid dissociation, so the K = [HF] / [H+][F-] = 1 / [H+][F-]/[HF] = 1 / Ka

the same applies for Ka and K of HSO4-.


K values for H+ + F- <==> HF is much larger than that for H+ + SO42- <==> HSO4-, F- prefers to dissolve and combine with H+ than SO42- does.