Non-metallic oxides dissolve in water to form

Which acid among the following has the highest $pK_a$ value?

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

$HNO_3$ in liquid hydrogen fluoride behaves as:

In the reaction $HBr + H_2O \rightleftharpoons H_3O^{+} + Br^{-}$,the conjugate base of the weak acid is .......

The first and second dissociation constants of an acid $H_2A$ are $1.0 \times 10^{-5}$ and $5.0 \times 10^{-10}$ respectively. The overall dissociation constant of the acid will be