The conjugate acid of $HPO_4^{2-}$ is

The conjugate base of $HSO_3^-$ is ......

Which of the following is an amphoteric substance?

Which of the following represents the correct increasing order of $pK_a$ values?

Which one of the following can be classified as a Bronsted base?

Values of dissociation constant,$K_a$ are given as follows:

Acid	$K_a$
$HCN$	$6.2 \times 10^{-10}$
$HF$	$7.2 \times 10^{-4}$
$HNO_2$	$4.0 \times 10^{-4}$

Correct order of increasing base strength of the bases $CN^{-}$,$F^{-}$ and $NO_2^-$ will be: