What is the ratio of the velocity of an electron in the ground state of a hydrogen atom to the velocity of an electron in the second excited state of $He^{+}$?

Binding energy of a hydrogen atom is $13.6 \ eV$. The binding energy of a singly ionized helium atom is : ............ $eV$

The energy difference of two stable orbits of Hydrogen is $214.68 \ kJ \ mol^{-1}$. If the transition of an electron takes place,find the emitted frequency. (Note: $v = \Delta E/h$ and $h = 6.626 \times 10^{-34} \ J \ s$)

Which of the following orders is $NOT$ correct for the $1^{st}$,$2^{nd}$,and $3^{rd}$ orbits of a hydrogen-like atom?

If $\lambda_0$ and $\lambda$ are the threshold wavelength and the wavelength of incident light,respectively,the velocity of the photoelectron ejected from the metal surface is:

Bohr’s model of atom explains :