The $pK_a$ of a weak acid $(HA)$ is $4.5$. The $pOH$ of an aqueous buffer solution of $HA$ in which $50\%$ of the acid is ionized is

An acidic buffer is obtained on mixing

Observe the following four solutions :
$P : 10 \ mL, 0.1 \ M \ NaOH + 5 \ mL, 0.1 \ M \ HCl$
$Q : 10 \ mL, 0.1 \ M \ NaOH + 15 \ mL, 0.1 \ M \ CH_3COOH$
$R : 10 \ mL, 0.1 \ M \ NH_3 + 10 \ mL, 0.1 \ M \ NH_4Cl$
$S : 10 \ mL, 0.05 \ M \ NaF + 5 \ mL, 0.1 \ M \ HF$
Which of above solutions act as buffer?

In some solutions,the concentration of $H_3O^{+}$ remains constant even when small amounts of strong acid or strong base are added to them. These solutions are known as

During the titration of $N/10$ acetic acid with $N/10 \, NaOH$,what is the $pH$ of the solution when $25\%$,$50\%$,and $75\%$ of the titration is complete? $[K_a = 10^{-5}]$

$0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ is mixed with $0.08 \ mol$ of $HCl$ and diluted to $1 \ L$. What will be the $[H^{+}]$ concentration in the solution?