The chemical characteristics or reactivity of an element depend mostly on the __________.

• A. number of electron shells present in the atoms
• B. mean energy level of its electrons
• C. degree to which it has more or fewer electrons than protons
• D. number of electrons in its outermost shell

Answer: (D)

Verified step by step guidance

1. Understand that the chemical characteristics or reactivity of an element are primarily determined by its electrons, specifically those in the outermost shell, known as valence electrons.
2. Recall that valence electrons are responsible for forming chemical bonds with other atoms. The number of valence electrons determines how an element interacts with other elements.
3. Consider the periodic table, where elements are organized by increasing atomic number. Elements in the same group (column) have the same number of valence electrons, which explains their similar chemical properties.
4. Recognize that the number of electron shells and the mean energy level of electrons can influence an atom's size and ionization energy, but the reactivity is most directly related to the valence electrons.
5. Conclude that the degree to which an atom has more or fewer electrons than protons affects its charge, but the chemical reactivity is primarily determined by the number of electrons in the outermost shell.