The correct answer to this question is this one:
HF (hydrofluoric acid) is a weak acid.
SO4 2- (sulfite ion) is a weak base
F- (fluoride anion) is a very weak base
HSO4 - (hydrogen sulfate) is a weak acid
Conjugate acid of HF = H2F+ (dihydrogen fluoride)
Conjugate base of HF = F- (fluoride)
Conjugate acid of SO4 2- = HSO4- (hydrogen sulfite)
SO4 2- does not have a conjugate base because you can't take away any H+
Conjugate acid of F- = HF (hydrofluoric acid)
F- does not have a conjugate base because you can't take away any H+
Conjugate acid of HSO4- = H2SO4 (sulphuric acid)
Conjugate base of HSO4- = SO4 2- (sulfite)
In very simple words:
Conjugate acid --> you add an H+
Conjugate base --> you take away an H+
