$pH$ of a resulting solution prepared by mixing $100 \ mL$ $0.1 \ M$ $HCl$ and $200 \ mL$ $0.05 \ M$ $NaOH$ is

$A$ solution of $0.1 \ M$ weak base $(B)$ is titrated with $0.1 \ M$ of a strong acid $(HA)$. The variation of $pH$ of the solution with the volume of $HA$ added is shown in the figure below. What is the $pK_{b}$ of the base? The neutralization reaction is given by $B + HA \rightarrow BH^{+} + A^{-}$.

If the equilibrium constant of $CH_3COOH + H_2O \rightleftharpoons CH_3COO^{-} + H_3O^{+}$ is $1.8 \times 10^{-5}$,what is the equilibrium constant for the reaction $CH_3COOH + OH^{-} \rightleftharpoons CH_3COO^{-} + H_2O$?

What is the $[OH^-]$ in the final solution prepared by mixing $20.0 \ mL$ of $0.050 \ M \ HCl$ with $30.0 \ mL$ of $0.10 \ M \ Ba(OH)_2$?

When $100 \, mL$ of $M/10 \, NaOH$ solution and $50 \, mL$ of $M/5 \, HCl$ solution are mixed,the $pH$ of the resulting solution would be:

Assuming complete dissociation,which of the following aqueous solutions will have the same $pH$ value?