For two acids $A$ and $B$,the values of $pK_{a1} = 1.2$ and $pK_{a2} = 2.8$ are given. Which of the following is correct?

$pH$ value of a solution,whose hydronium ion concentration is $6.2 \times 10^{-9} \ mol/L$,is

The $pH$ of a $0.01 \, M$ solution of acetic acid having a degree of dissociation of $12.5 \%$ is:

An organic monobasic acid has a dissociation constant of $2.25 \times 10^{-6}$. What is the percent dissociation in its $0.01 \ M$ solution (in $\%$)?

Consider the dissociation equilibrium of the following weak acid $HA \rightleftharpoons H^{+}_{(aq)} + A^{-}_{(aq)}$. If the $pK_{a}$ of the acid is $4$, then the $pH$ of $10 \ mM$ $HA$ solution is . . . . . . . (Nearest integer)
[Given : The degree of dissociation can be neglected with respect to unity]

The $K_b$ of ammonia $(NH_3)$ is $1.8 \times 10^{-5}$ at $298 \ K$. Calculate the $pH$ of a $0.1 \ M$ ammonia solution. (in $.13$)