The number which most likely represents the first ionization energy (in kilocalories per mole of atoms) for a nonmetallic element is: 4. 239.
First ionization energy can be defined as the minimum energy that is required to remove (detach) the outermost electron from a neutral atom in its gaseous state.
In Chemistry, the first ionization energy is usually expressed as kilocalories per mole of atoms (kcal/mol) or kilojoules per mole of atoms (kJ/mol).
On a periodic table, the ionization energy of chemical elements tend to increase from left to right across a period and from bottom to top in each group.
Based on scientific calculations, 239 kcal/mol is the first ionization energy for sulfur (S), which is a nonmetallic element.
In conclusion, the number which most likely represents the first ionization energy (in kilocalories per mole of atoms) for a nonmetallic element is 239.
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