Answer
The statement (c) is true.
Work Step by Step
(a) and (d):
If ($HA$) were a strong acid:
$[H_3O^+] = 0.10M$
$pH = -log 0.10 = 1$
But, since it is a weak acid:
$[H_3O^+] < 0.10M$
pH $\gt$* 1
* Since pH is the NEGATIVE logarithm, we change its direction.
pH $\gt$ 1: Therefore, (a) and (d) are false.
(b) and (c)
For pure acid solution, ignoring the $[H_3O^+]$ (It's a very small number), $[H_3O^+] = [A^-]$, because when $[HA]$ dissociates, it equally produces $H^+$ and $A^-$.
Therefore: $(b) : False,(c) : True$
