Answer
(a) $Li^+$ is pH-neutral;
(b) $CH_3N{H_3}^+$ is a weak acid;
(c) $Fe^{3+}$ is a weak acid.
Work Step by Step
(a) $Li^{+}$ is the cation of a strong base $(LiOH)$, therefore, it is pH-neutral.
(b) $CH_3N{H_3}^+$ is the conjugate acid of a weak base $(CH_3NH_2)$. Thus, it is a weak acid.
(c) $Fe^{3+}$ is a small and highly charged metal cation. Thus, it is a weak acid.
