What's the deal with wavelengths emitted by mercury and hydrogen?

Question

Please explain why the much more complex atom of Hg shows only a few lines more than the simplest atom, hydrogen.

Answer 1

Excellent question. Mercury has rather more lines altogether (291 in NIST database vs 167), but some of them are very close together, and a lot of them are in the infrared.

I suppose the answer is that even for mercury, most observed lines involve just one outermost electron.