The following elements should have optical spectra similar to either a hydrogen atom or a helium atom. Indicate which of the following elements should have optical spectra similar to a helium atom. (Select all that apply.)
The choices are: Cadmium, Lithium, Technetium, Titanium, Platinum, Strontium, Calcium, and Francium.
The Attempt at a Solution
I thought that since helium has a full level of valence electrons, it would have similar optical spectra as other elements with their highest orbitals completely filled. So I went with Strontium and Calcium, but this is incorrect. What am I doing wrong? Any help would be much appreciated.