Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Terbium (IV) acts as an oxidant in aqueous solution. Reason (R): The +4 oxidation state of Terbium is favoured by its noble gas core electronic configuration. In the light of the above statements, choose the most appropriate answer from the options given below:

Step-by-step solution

Assertion (A) is correct: Terbium (Tb) can show a +4 oxidation state, but the most stable oxidation state for all lanthanoids is +3 . Thus, Tb⁴⁺ readily accepts an electron to become Tb³⁺ , acting as a strong oxidant in aqueous solutions. Reason (R) is incorrect: The atomic number of Terbium is 65 . The electronic configuration of Tb is [Xe] 4f⁹ 6s² . In the +4 oxidation state, the configuration of Tb⁴⁺ is [Xe] 4f⁷ . This represents a stable half-filled f -subshell, not a noble gas core configuration (which would b