Which of the following electronic configurations is correct?

Krypton $(_{36}Kr)$ has the electronic configuration $(_{18}Ar) \ 4s^2, 3d^{10}, 4p^6$. The $37^{th}$ electron will go into which one of the following sub-levels?

Which of the following sets of quantum numbers is impossible for an electron?

Paramagnetic substances must contain .....

Select the correct statements for quantum numbers.
$(i)$ Magnetic quantum number $(m_l)$ gives information about the spatial orientation of orbitals with respect to the standard set of coordinate axes.
$(ii)$ Electron spin quantum number is represented by '$s$' and has values of $\pm \frac{1}{2}$.
$(iii)$ Principal quantum number $(n)$ determines the size of the orbitals and also,to a large extent,the energy of the orbitals.

Explain the stability of completely filled and half-filled subshells by giving reasons.