Why is europium (II) more stable than cerium (II) ?

Why is equropium (II) more stable than cerium (II) (Eu = 63, Ce =58) give one reason.

Explain the following: (a) Europium (II) is more stable than cerium (II) (b) Zr and Hf exhibit similar properties. ( c) Scandium forms no coloured ions, yet it is regarded as a transition metal.

Why is nitrogen more stable than oxygen?