If a solution has $pOH$ value $12$ at $25\,^{\circ}C$,$H^{+}$ concentration should be

Observe the following solutions:
$I$. Black coffee
$II$. $0.2 \ M \ NaOH$
$III$. Lemon juice
$IV$. Lime water
$V$. Human Saliva
$VI$. Tomato juice
The number of solutions with $pH$ less than $7$ is

The $pH$ of a solution is $5.0$. To this solution,sufficient acid is added to decrease the $pH$ to $2.0$. The increase in hydrogen ion concentration is $...$ times.

An aqueous solution whose $pH = 0$ is

At a certain temperature,if $pK_w = 12.60$,then which of the following is correct for an acidic solution?

Find the concentration of $(OH^-)$ in a solution with $pH = 3.3$.