Question

Sodium atom has lower electron affinity than chlorine atom why?

Answer 1

ELECTRON AFFINITY
When an negative ion or electron is added to a neutral atom of an element then the change in energy by releasing  energy is called electron affinity or we can say the amount of energy released due to addition of electron to neutral atom .

Since due to non-metal electronic configuration it gains electron and vice-vera with metals .Since chlorine is a non-metal and sodium is a metal so Sodium atom has lower electron affinity than chlorine atom.