For a $H$ atom,the wavelength for the highest energy transition is $91.2 \ nm$. Calculate the corresponding wavelength for $He^{+}$ in $nm$.

In the Bohr model of the atom,when an electron undergoes a transition from $n = 1$ to $n = 3$,the energy absorbed or emitted is ........

Which transition in the hydrogen spectrum would have the same wavelength as the Balmer type transition from $n = 4$ to $n = 2$ of $He^+$ spectrum?

Which of the following corresponds to the energy of a possible excited state of hydrogen (in $eV$)?

When a hydrogen sample in the ground state is bombarded with electrons,what potential is required to accelerate the electrons so that the first Brackett line is emitted? $(eV)$

What is the ratio of the radii of the second orbit for $H$,$He^{+}$,and $Li^{2+}$?