a
(a)\(Tl^+\) ions are more stable than \(Tl^{3+}\) and thus, \(Tl^{3+}\) ions change to \(Tl^+\) ions thereby acting as oxidising agents.
\(Tl^{3+}\) compounds \(+ 2e^- \) \(\to\)\(Tl^+\) compounds
(less stable oxidising agent) (more stable oxiding agent)