Final answer:
The electrons in the outer shell most strongly govern the properties of an atom, with valence electrons determining an atom's reactivity. The strong nuclear force, while essential for nuclear stability, does not directly influence the behavior of electrons.
Step-by-step explanation:
The elements that exert the strongest controls on the properties of an atom are the electrons in the outer shell. These electrons are crucial in determining how an atom will interact with other atoms and participate in chemical reactions. The valence shell, being the atom's outermost shell, when full, makes an atom stable, and when not full, makes it reactive. The number of valence electrons in the outer shell therefore dictates an atom's chemical properties and reactivity.
As for the influence of the strong nuclear force on the electrons, it does not directly have any influence on them. The strong nuclear force acts to counteract the repulsive Coulomb forces between protons in the nucleus, providing the necessary stability for the nucleus despite the electrostatic repulsion between the positively charged protons. This force is crucial for nuclear stability but does not impact the behavior of electrons around the nucleus.