What is the radius of the fourth orbit of $Be^{3+}$ (in $pm$)?

For a hydrogen atom,the energy of an electron in the first excited state is $-3.4 \ eV$. The kinetic energy $(KE)$ of the same electron in the hydrogen atom is $x \ eV$. The value of $x$ is . . . . . . $\times 10^{-1} \ eV$. (Nearest integer)

If the wavelength of light is $5.89 \times 10^{-5} \ cm$,then the energy of one photon in the given light will be ......

The ratio of minimum wavelengths of Lyman and Balmer series will be $:-$

The number of maximum possible different spectral lines obtained in the Balmer series,when an electron makes a transition to the ground state from the $5^{th}$ excited state in a sample of hydrogen atoms,is:

The radius ratio of Bohr's first orbit of hydrogen-like species $He^{+}$,$Li^{2+}$,and $Be^{3+}$ is: