Due ta strong inert pair effect, the +3 oxidation state of Tl is less stable than its +1 oxidation state. Since in Tl(NO3)3 , oxidation state of Tl is +3, therefore, it can easily gain two electrons to form TlNO3 in which the oxidation state of Tl is +1. Consequently, Tl(NO3)3 acts as an oxidising agent.
