The given blank can be filled with valence electrons.
Explanation:
In chemistry, an outer shell electron known as a valence electron is linked to an atom. This electron can take part in the production of a chemical bond if the external shell is not closed. The existence of valence electrons can assist in finding the chemical properties of an element, that is, whether it take part in bond formation with other elements, and if so, how easily and with how many. A valence electron can be found only in the outmost electron shell in case of the main group element and is found in an inner shell in case of a transition metal.
