In the case of a hydrogen atom,which of the following transitions does not involve the absorption or emission of energy?

Total number of ions from the following with noble gas configuration is . . . . . . .
$Sr^{2+} (Z=38), Cs^{+} (Z=55), La^{2+} (Z=57), Pb^{2+} (Z=82), Yb^{2+} (Z=70) \text{ and } Fe^{2+} (Z=26)$

The spin of the electron:

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.

Which of the following electronic configurations is incorrect?

The number of electrons with magnetic quantum number,$m_l=0$ in the elements with atomic numbers $Z=24$ and $Z=29$ are respectively