Bohr's atomic model explains the spectra of single-electron atoms like \\\\(H\\\\)-atom. It does not explain the spectra of multi-electron atoms. So the atoms which are isoelectronic and have the same electronic configuration are well explained by this atomic model.\\\\(He^+\\\\), \\\\(Li^{2+}\\\\) and tritium \\\\(_{ 1 }{ H }^{ 3 }\\\\) have same number of electrons as that of hydrogen atom i.e. \\\\(1\\\\) while \\\\(Be^{2+}\\\\) is formed by losing \\\\(2e\\\\). So, it is a two-electron system.Option D is correct.