Which electronic level would allow the hydrogen atom to absorb a photon but not to emit a photon?

Arrange the electrons represented by the following sets of quantum numbers in the decreasing order of energy.
$(i) \ n = 4, l = 0, m_l = 0, m_s = +\frac{1}{2}$
$(ii) \ n = 3, l = 1, m_l = 1, m_s = -\frac{1}{2}$
$(iii) \ n = 3, l = 2, m_l = 0, m_s = +\frac{1}{2}$
$(iv) \ n = 3, l = 0, m_l = 0, m_s = -\frac{1}{2}$

What is the number of unpaired electrons in the electronic configuration of the $N^{+2}$ ion?

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

Choose the correct alternatives. The number of unpaired electrons in an atom of:

Possible number of orientations of a subshell is