Answer: Reactivity
Step-by-step explanation:
The location of electrons in an atom defines the reactivity of the atom. The number of electrons that is found in the outermost shell defines its reactivity.
The tendency of an atom to take part in a chemical reaction is defined as reactivity.
Noble gases have low reactivity because they have valence electrons in the outermost shell.
The atoms that have not completed their octet are not stable and have high reactivity. Example: chlorine , fluorine