The tendency of an element to react is closely related to

Aits atomic mass.
Battractions between its atoms.
Cthe number of valence electrons in atoms of the element.
Dthe ratio of protons to neutrons in atoms of the element

Verified Answer :

The tendency of an element to react is closely related to the number of valence electrons in atoms of the element. 

The valence electrons are what determine how an atom would bond, and when it would bond, and also its reactivity toward other atoms. 

The answer to the question is C.