Why CB configuration is seldom used?

The d^1 configuration is very unstable in transition metal ions. Explain why ?

Why does a configuration of charges possess potential energy?

Why are elements having ns^(2)np^(6) configuration called noble gases?

Explain: Why should contraceptives be used ?

Answer the following: Copper (I) has d^10 configuration while copper (II) has d^9 configuration, still copper (II) is more stable in aqueous solution than copper (I). Why?