Assign $A, B, C, D$ for the given type of reaction:
$Mg(OH)_2 \downarrow + 2HCl \longrightarrow MgCl_2 + 2H_2O$

When $200 \ mL$ solution of $HCl$ of $pH=2$ is mixed with $300 \ mL$ solution of $NaOH$ of $pH=12$,the $pH$ of resulting solution is $(\log 2=0.3)$

$A$ soft drink was bottled with a partial pressure of $CO_2$ of $3 \ bar$ over the liquid at room temperature. The partial pressure of $CO_2$ over the solution approaches a value of $30 \ bar$ when $44 \ g$ of $CO_2$ is dissolved in $1 \ kg$ of water at room temperature. The approximate $pH$ of the soft drink is............... $\times 10^{-1}$ (First dissociation constant of $H_2CO_3 = 4.0 \times 10^{-7}$; $\log 2 = 0.3$; density of the soft drink $= 1 \ g \ mL^{-1}$)

When $100 \ mL$ of $0.1 \ M$ $NaCN$ solution is titrated with $0.1 \ M$ $HCl$ solution,the variation of $pH$ of the solution with the volume of $HCl$ added will be:

The dissociation constant of pure water at $18\,^oC$ will be .......... (Degree of dissociation of pure water at $18\,^oC = 1.8 \times 10^{-9}$)

By adding $20 \ mL$ $0.1 \ N$ $HCl$ to $20 \ mL$ $0.1 \ N$ $KOH$,the $pH$ of the obtained solution will be