The pairs of compounds which cannot exist together in aqueous solution are :
$I. NaH_2PO_4$ and $Na_2CO_3$ $II. Na_2CO_3$ and $NaHCO_3$
$III. NaOH$ and $NaH_2PO_4$ $IV. NaHCO_3$ and $NaOH$

The ionization constant of dimethylamine is $5.4 \times 10^{-4}$. Calculate its degree of ionization in its $0.02 \ M$ solution. What percentage of dimethylamine is ionized if the solution is also $0.1 \ M$ in $NaOH$?

Find the resulting $pH$ of the mixture of $200 \ mL$ of $HCl$ $(pH = 2)$ and $300 \ mL$ of $NaOH$ $(pH = 12.0)$.

When $NaCl$ is dissolved in water,the sodium ion is

$A$ weak acid is titrated with a weak base. Consider the following statements regarding the $pH$ of the solution at the equivalence point.
$(i)$ $pH$ depends on the concentration of acid and base
$(ii)$ $pH$ is independent of the concentration of acid and base
$(iii)$ $pH$ depends on the $pK_{a}$ of acid and $pK_{b}$ of base
$(iv)$ $pH$ is independent of the $pK_{a}$ of acid and $pK_{b}$ of base
The correct statements are

Calculate the molar solubility of $AgCl$ at $25\,^oC$ in $3.0\ M\ NH_3$ ($K_{sp}$ of $AgCl = 2.0 \times 10^{-10}$,$K_f$ of $[Ag(NH_3)_2]^+ = 1.25 \times 10^7$) (in $M$)