Why `Sm^(2+)`, `Eu^(2+)` and `Yb^(2+)` in solutions 'are good reducing agents but an aqueous solution of `Ce^(4+)` is a good oxidising agent?

Explanation

Reducing agent is.one whịch has a strong tendency.for oxjdation. Most stable oxidation state of lanthanides is +37 Hence ions, in +2 state havé strong tendency for oxidation and get cónverted into +3 state. Hence they act as reducing agents. .(Ce)^(4+). has tendency to get reduced to .(Ce)^(+3). Theiefore Ce .^(i). acts as an oxidising agent. "H. (Reducing agent undergoes.oxidation:
oxidising agent undergoes reduction)