Question

What is valence electron ?

Answer 1

The valence electrons are the electrons in the outermost shell or energy level of an atom. They are typically the electrons which are involved in forming bonds with other atoms. The electrons in the inner shells do not interact much with other atoms or molecules.

The reacting power of an element depends on the number of electrons in the outer most shell/energy level. If it is completely filled to capacity like in case of Helium, Argon, Krypton etc., then the element does not react with other atoms.