Question

the chemical behavior of an atom is determined by the

size of the atom.
mass of the nucleus.
outermost electron shell.
number of protons.
number of neutrons.

Explanation:

The outermost electron shell, also known as the valence shell, is involved in chemical bonding and interactions. Atoms tend to gain, lose, or share electrons to achieve a stable electron - configuration in this shell, which determines their chemical behavior.

Answer:

outermost electron shell.