Which metal ion produces the light with the highest energy?

Question

a. Na+
b. Ca+
c. K+
d. Ba2+

Answer 1

Actually the question is quite broad; there are no indications of the kind of excitation sources used. Assuming we are talking about using flame emission, I think Na^+, K^+, and Ba^2+ leads to closed shells (noble gas structure)and that makes me think Ca^+ is the only one with an electron that could be moved easily to an outer shell.