the number of valence electrons. the ratio of protons to neutrons. how tightly atoms are packed. the number of neutrons in atoms.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: The tendency of an element to react chemically is closely related to
Possibilities:
- the number of valence electrons.
- the ratio of protons to neutrons.
- how tightly atoms are packed.
- the number of neutrons in atoms.

the number of valence electrons.