Five solutions $A, B, C, D$ and $E$ when tested with universal indicator showed $pH$ values of $4, 1, 11, 7$ and $9$,respectively. Which solution is:
$(a)$ neutral?
$(b)$ strongly alkaline?
$(c)$ strongly acidic?
$(d)$ weakly acidic?
$(e)$ weakly alkaline?
Arrange the $pH$ values in increasing order of hydrogen-ion concentration.

(A) Neutral: Solution $D$ $(pH = 7)$.
$(b)$ Strongly alkaline: Solution $C$ $(pH = 11)$.
$(c)$ Strongly acidic: Solution $B$ $(pH = 1)$.
$(d)$ Weakly acidic: Solution $A$ $(pH = 4)$.
$(e)$ Weakly alkaline: Solution $E$ $(pH = 9)$.
The concentration of hydrogen ions $[H^+]$ is inversely proportional to the $pH$ value. Therefore,the increasing order of hydrogen-ion concentration is:
$pH \, 11 < pH \, 9 < pH \, 7 < pH \, 4 < pH \, 1$ (i.e.,$C < E < D < A < B$).