Values of dissociation constant, K_a are given as follows: Correct order of increasing base strength of the base CN^-, F^- and NO_2^- will be:

Values of dissociation constant, $\displaystyle \mathrm{K}_{\mathrm{a}}$ are given as follows :

Acid	$\displaystyle \mathrm{K}_{\mathrm{a}}$
HCN	$\displaystyle 6.2 \times 10^{-10}$
HF	$\displaystyle 7.2 \times 10^{-4}$
$\displaystyle \mathrm{HNO}_2$	$\displaystyle 4.0 \times 10^{-4}$

Correct order of increasing base strength of the base $\displaystyle \mathrm{CN}^{-}, \mathrm{F}^{-}$and $\displaystyle \mathrm{NO}_2^{-}$will be :