Which of the following elements has a completely filled $4f$ orbital in its ground state electronic configuration?

To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.

In the electronic configuration of which of the given elements,$Aufbau$ principle or $(n+l)$ rule is violated?

$d$-block elements form

Which electrons are involved in achieving higher oxidation states by transition metals?

What is the difference in atomic volume between $Au$ and $Cu$ in $22$ carat gold jewelry?