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: $(b) : False,(c) : True$