The +3 oxidation state is the most characteristic for lanthanides, but +2 and +4 states can also occur due to the stability of empty, half-filled, or completely filled f-subshells. Identify the pair of ions ( P , Q ) where P acts as a strong oxidizing agent despite having a half-filled 4 f subshell, and Q acts as a strong reducing agent despite having a completely filled 4 f subshell. [Given atomic numbers: Ce =58, E

Step-by-step solution

An ion acts as an oxidizing agent if it tends to gain electrons to reach the more stable +3 state. This means the ion must be in a higher oxidation state, such as +4 . We are given that P is an oxidizing agent with a half-filled 4 f subshell ( 4 f ⁷ ). Assuming P is in the +4 state: Z_ P - 54 - 4 = 7 Z_ P = 65 The element with atomic number 65 is Terbium ( Tb ). Thus, P is Tb ⁴⁺ . An ion acts as a reducing agent if it tends to lose electrons to reach the stable +3 state. This means the ion must be in a lower oxidat