The most probable radius (in $pm$) for finding the electron in $He^{+}$ is

The total energy of the electron of $H^{-}$ atom in the second quantum state is $-E_2$. The total energy of the $He^{+}$ atom in the third quantum state is

How does the energy gap between successive energy levels in an atom vary from low to high $n$ values?

The $I.P.$ of a hydrogen-like species is $36 \ eV$. What is the value of the second excitation energy in $eV$?

The spectral series formed when electrons of excited hydrogen atoms return to the third orbit from higher energy orbits is

The quantum theory was first used to explain the structure of the atom,which was proposed by .......