Three acidic solutions $A, B$ and $C$ have $pH = 0, 3$ and $5$ respectively.
$(i)$ Which solution has the highest concentration of $H^{+}$ ions?
$(ii)$ Which solution has the lowest concentration of $H^{+}$ ions?

(A) $(i)$ Solution $A$ with $pH = 0$ has the highest concentration of $H^{+}$ ions because $pH$ is inversely proportional to the concentration of $H^{+}$ ions $(pH = -\log[H^{+}])$.
$(ii)$ Solution $C$ with $pH = 5$ has the lowest concentration of $H^{+}$ ions because it has the highest $pH$ value among the given solutions.