What is the wave number of a photon emitted during the transition from orbit $n=4$ to $n=2$ in a hydrogen atom (in $cm^{-1}$)? $[R_{H}=109677 \ cm^{-1}]$

What is the wave number of the lowest energy transition in the Balmer series?

In Bohr's model,the atomic radius of the first orbit is $\gamma$. The radius of the $3^{rd}$ orbit is:

The statements
$i$. In filling a group of orbitals of equal energy,it is energetically preferable to assign electrons to empty orbitals rather than pair them into a particular orbital.
$ii$. When two electrons are placed in two different orbitals,energy is lower if the spins are parallel.
Are valid for

Which of the following statements regarding the energy of the stationary state is true in the following one-electron system?

If the ionization potential of $Li^{2+}$ is $122.4 \ eV$,what is the $5^{th}$ ionization potential of carbon in $eV$?