In a sample of hydrogen atom in ground state electrons make transition from ground state to a particular excited state where path length is five times to de-Broglie wavelength, electrons make back transition to the ground state producing all possible photons. If photon having $2^{\mathrm{nd}}$ highest energy of this sample can be used to excite the electron in a particular excited state of ${\mathrm{Li}}^{2+}$ atom then find the final excited state of ${\mathrm{Li}}^{2+}$ atom.