Which electronic arrangement shows the ground state of an element?

Statement $A$: An orbital can accommodate a maximum of two electrons.
Reason $R$: Two electrons in an orbital produce opposite magnetic fields.

What would be the electronic configuration of $Cs (Z=55)$ in each case?
$(a)$ If there were three possibilities of the electron spin.
$(b)$ If the quantum number,$l$,could have the value $n$,and if all the rules governing electron configuration were otherwise valid.

How many unpaired electrons will be present in the ground state of an atom which has valence electronic configuration $3d^6$ in its $+3$ oxidation state?

The set of principal $(n)$,azimuthal $(l)$ and magnetic $(m_l)$ quantum numbers that is not allowed for the electron in $H$-atom is

What is the atomic number of the element with $M^{2+}$ ion having electronic configuration $[Ar] 3d^8$?