The conjugate base of $H_{2}PO_{4}^{-}$ is:

Which one of the following is not a base?

Which of the following compounds can act as both a $Br\o nsted$ acid and a $Br\o nsted$ base?

The one which has the highest value of $pH$ is

Which among the following is $NOT$ a Lewis acid?

The species: $H_{2}O$,$HCO_{3}^{-}$,$HSO_{4}^{-}$,and $NH_{3}$ can act both as Bronsted acids and bases. For each case,give the corresponding conjugate acid and base.