When the azimuthal quantum number has a value of $l = 1$,the shape of the orbital is

Statement $A$: In a potassium atom,the $19^{th}$ electron enters the $4s$-orbital instead of the $3d$-orbital.
Reason $R$: The $(n + l)$ rule is followed to determine the minimum energy of an orbital.

$A$ completely filled $d$-orbital $(d^{10})$ configuration is:

The correct order of increasing energy of atomic orbitals is

An element has $d^5$ configuration. The total number of electron exchanges possible for it is

Which of the following sets of quantum numbers is not valid?