Which solution contains maximum number of ${H^ + }$ ion

A compound whose aqueous solution will have the highest $pH$

The ionization constant of $HF$, $HCOOH$ and $HCN$ at $298\, K$ are $6.8 \times 10^{-4}, 1.8 \times 10^{-4}$ and  $4.8 \times 10^{-9}$ respectively. Calculate the ionization constants of the corresponding conjugate base.

${K_b}$ of $N{H_4}OH = 1.8 \times {10^{ – 5}}$ calculate $pH$ of $0.15$ $mol$ $N{H_4}OH$ and $0.25$ $mol$ $N{H_4}OH$ containing solution.

The ${K_b}$ of ammonia is $1.8 \times {10^{ – 5}}$ at $298$ $K$ temperature. Calculate the $pH$ of $0.1$ $M$ solution.