The compound that is not a Lewis acid is

Identify the conjugate acid-base pair respectively from the following equilibrium reaction.
$HPO_{4(aq)}^{2-} + H_2O_{(\ell)} \rightleftharpoons PO_{4(aq)}^{3-} + H_3O_{(aq)}^{+}$

In the reaction $2H_2O \rightleftharpoons H_3O^{+} + OH^{-}$,water is

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

The strongest Bronsted base among the following anions is:

Consider the following data for a series of hydrogen halide Bronsted acids:-

Acid	$HF$	$HCl$	$HBr$	$HI$
$K_a$	$7.2 \times 10^{-4}$	$1 \times 10^6$	$1 \times 10^9$	$3 \times 10^{11}$

Which of these Bronsted acids would have the weakest conjugate base?