Which one of the following represents an impossible arrangement of quantum numbers?

The number of $d-$ electrons in $Fe^{2+} \ (Z = 26)$ is not equal to the number of electrons in which one of the following?

If the electronic configuration of a nitrogen atom were $1s^7$,its energy would be lower than the ground state configuration $1s^2 2s^2 2p^3$ because the electrons would be closer to the nucleus. However,the configuration $1s^7$ is not observed. Which of the following principles is violated?

Number of unpaired electrons in $Fe^{+3}$ $(Z = 26)$ is

Identify the element if its expected electronic configuration is $[Ar] 3d^{10} 4s^{2}$.

The number of radial nodes and angular nodes of a $4f$-orbital are respectively: