The $39^{th}$ electron of an element enters which of the following subshells?

What is the maximum number of electrons that can have the quantum numbers $n = 5$ and $m_l = +2$?

Which of the following transitions are allowed in the normal electronic emission spectrum of an atom?

Arrange the energy of the $2s$ orbital in the following atoms in decreasing order: $H, Li, Na, K$.

If an atom has $13$ electrons in the $M$ shell and $1$ electron in the $N$ shell,then the number of unpaired electrons in that atom is ...

The ground state energy of a hydrogen atom is $-13.6 \ eV$. Consider an electronic state $\Psi$ of $He^+$ whose energy,azimuthal quantum number,and magnetic quantum number are $-3.4 \ eV$,$2$,and $0$ respectively. Which of the following statement$(s)$ is(are) true for the state $\Psi$?
$(1)$ It has $2$ angular nodes
$(2)$ It has $3$ radial nodes
$(3)$ It is a $4d$ state
$(4)$ The nuclear charge experienced by the electron in this state is less than $2e$,where $e$ is the magnitude of the electronic charge.