Which of the following orders of relative strength of acid is correct?

The conjugate base of a strong acid is a

Which of the following equilibria represents a $Lewis$ acid-base reaction but not a $Br\o nsted$ acid-base reaction?

In the reaction $HC_2O_4^{-} + PO_4^{3-} \rightarrow HPO_4^{2-} + C_2O_4^{2-}$,which are the two Brønsted bases?

For the following two acid-base reactions,which statement is True?
$(I) CH_3CH_2^- + CH_3NH_2$ $(pK_a = 35)$ $\rightleftharpoons CH_3CH_3$ $(pK_a = 50)$ $+ CH_3NH^-$
$(II) F^- + H_2O$ $(pK_a = 15.7)$ $\rightleftharpoons HF$ $(pK_a = 3.2)$ $+ HO^-$

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