What is the nature of an aqueous solution of ammonia?

Which of the following statements is correct?

Which one is the weakest acid?

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

What is the conjugate base of $OH^{-}$?

The $K_{a}$ values of $A$,$B$,and $C$ are $1.8 \times 10^{-4}$,$5 \times 10^{-10}$,and $3 \times 10^{-8}$ respectively. The correct order of their acidic strength is