Why `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.

(a) Separation of lanthanide elements is difficult. Explain. (b) 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?

Why is aluminium a good reducing agent ? Give examples.

Between Cr^(2+) and Fe^(2+) which is a stronger reducing, agent in aqueous solution and why?

Alkali metals are good reducing agents because they easily:

H_2O_2 acts as an oxidising agent in:

H_2O_2 acts as a reducing agent in its:

H_2S acts only as a reducing agent but SO_2 acts as a reducing as well as oxidising agent. Why?