Why is it easier to remove an electron from sodium atom than a chlorine atom?

It is easier to remove an electron from a sodium atom than from a chlorine atom because sodium has a single valence electron in its outer shell, which is more loosely held and experiences less effective nuclear charge. In contrast, chlorine has seven valence electrons and a higher effective nuclear charge, meaning its outer electrons are held more tightly. Consequently, removing an electron from sodium requires less energy compared to chlorine.