Question

$$Sm^{2+}$$, $$Eu^{2+}$$ and $$Yb^{2+}$$ ions in solutions are good reducing agents but an aqueous solution of $$Ce^{4+}$$ is a good oxidising agent. Why?

Answer 1

$$Sm^{2+}$$, $$Eu^{2+}$$ and $$Yb^{2+}$$ ions in solutions are good reducing agents as they tend to acquire common oxidation state of $$+3$$ shown by lanthanoids by the loss of one electron while $$Ce^{4+}$$ gains one electron to attain $$+3$$. Hence, $$Ce^{4+}$$ is an oxidising agent.