The element with the lowest ionization energy is CESIUM, CS.
Ionization energy is the energy required to remove the most loosely bound electron in an atom of an element. The higher the number of shells in an atom of an element, the lower the ionization energy that will be required to remove the valence electron.
A set of attainable values for some physical quantity such as energy or wavelength
I believe your answer is 23.
Credit: answers.yahoo.com
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Elements in the third row can break the octet rule
