Based on the quantum numbers, what will be the maximum number of elements in the sixth period of the periodic table?

On what does the energy of hydrogen and hydrogen-like species depend? On what does it not depend?

An element in $+2$ oxidation state has $24$ electrons. The atomic number of the element and the number of unpaired electrons in it respectively are

Considering the ground state of $Cr$ atom $(Z = 24)$,the number of electrons associated with azimuthal quantum numbers $l = 1$ and $l = 2$ are,respectively:

Which of the following statement$(s)$ is/are true?
$A$. If two orbitals have the same value of $(n+l)$, the orbital with lower value of $n$ will have lower energy.
$B$. Energies of the orbitals in the same subshell increase with increase in atomic number.
$C$. The size of $2p_x$ orbital is less than the size of $3p_x$ orbital.
$D$. Among $5f, 6s, 4d, 5p$ and $5d$ orbitals, none of the orbitals have $2$ radial nodes.

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