The number of $H^{+}$ ions present in $10 \ mL$ of a solution with $pH = 12$ is ........

Calculate $[OH^{-}]$ and $pH$ of a solution containing $[H^{+}] = 0.001 \ M$.

Calculate the hydrogen ion concentration in the following biological fluids whose $pH$ are given below:
$(a)$ Human muscle-fluid,$6.83$
$(b)$ Human stomach fluid,$1.2$
$(c)$ Human blood,$7.38$
$(d)$ Human saliva,$6.4$

If $[H_3O^+]$ of a solution is $1 \times 10^{-4} \text{ M}$, what is the value of $pOH$ at $298 \text{ K}$?

The definition of $pH$ is

$100 \ mL$ of $NaOH$ solution has a $pH = 10$. Calculate the concentration of hydroxide ions,$[OH^{-}]$.