Which is defined as the energy required to remove an electron from an atom of an element in the gaseous state?

Which is defined as the energy required to remove an electron from an atom of an element in the gaseous state?

Which is defined as the energy required to remove an electron from an atom of an element in the gaseous state? 




a. ionization energy
b. electronegativity
c. ionic radius
d. law of octets



Answer: A