Which one is the weakest acid?

The dissociation constants of two acids $HA_1$ and $HA_2$ are $3.14 \times 10^{-4}$ and $1.96 \times 10^{-5}$ respectively. The relative strength of the acids will be approximately:

$(i)$ $A$ strong acid has a weak conjugate base.
$(ii)$ An acid is an electron pair acceptor.
The above statements $(i)$ and $(ii)$ are:

Which of the following is a Lewis acid?

Which one of the following compounds is not a protonic acid?

Ammonium hydroxide is a weak base because