Answer 1

i. Cerium (Ce) and Terbium (Tb) show +4 oxidation states. Their electronic configurations are given below:

Ce = [Xe] 4f¹ 5d¹ 6s² ; Ce⁴⁺ = [Xe]

Tb = [Xe] 4f⁹ 6s²       ; Tb⁴⁺ = [Xe] 4f⁷

ii. It is clear from the configuration of Ce that Ce⁴⁺ is favoured by its noble gas configuration. But it can be easily converted into stable Ce³⁺ by a gain of an electron. Due to this reason, Ce⁴⁺ is a good oxidizing agent.

iii. Similarly, Tb⁴⁺ ion is stabilized due to a half-filled f-subshell. It can be easily converted into stable Tb³⁺ by gain of an electron. Due to this reason, Tb⁴⁺ is a good oxidizing agent.