Chemistry - Ionic Equilibrium Question with Solution | TestHub

Higher the value of ${\mathrm{K}}_a$ lower will be the value of ${\mathrm{pK}}_{\mathrm{a}}$ i.e. higher will be the acidic nature. Further since ${\mathrm{CN}}^{-},{\mathrm{F}}^{-}$and ${\mathrm{NO}}_2^{-}$are conjugate base of the acids $\mathrm{HCN},\mathrm{HF}$ and ${\mathrm{HNO}}_2$ respectively hence the correct order of base strength will be $${\mathrm{F}}^{-}<{\mathrm{NO}}_2^{-}<{\mathrm{CN}}^{-}$$ $(\because$ stronger the acid weaker will be its conjugate base)