Sodium an alkali metal and chlorine a halogen are both in period 3 of the periodic table which element has a higher ionization energy

Chlorine has higher ionization energy

Ionization energy is defined as the minimum amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated neutral gaseous atom, molecule or ion. It is quantitatively expressed in symbols as

X + energy → X+ + e−

Where X is any atom, molecule or ion capable of being ionized, X+ is that atom or molecule with an electron removed, and e− is the removed electron. This is generally an endothermic process.

The ionization energy of Sodium (alkali metal) is 496KJ/mol whereas Chlorine's first ionization energy is 1251.1 KJ/mol.  

Alkali metals (IA group) have small ionization energies, especially when compared to halogens.  Because as we move across the period from left to right, in general, the ionization energy increases. The atoms become smaller which causes the nucleus to have greater attraction for the valence electrons. Therefore, the electrons are more difficult to remove.

c, liquids evaporate, creating a gas

c. is the answer

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