The outer electronic structure $3s^23p^5$ is possessed by

Which of the following sets of quantum numbers is correct for an electron in a $4f$ orbital?

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

What is the number of $d$-electrons present in $Fe^{2+}$ ($Fe$ atomic number = $26$)?

If the given four electronic configurations:
$(i)$ $n=4, l=1$
$(ii)$ $n=4, l=0$
$(iii)$ $n=3, l=2$
$(iv)$ $n=3, l=1$
are arranged in order of increasing energy,then the order will be:

In the sixth period,the orbitals that are filled are