An atom with equal numbers of positive and negative particles is called a

• A. Neutral Atom
• B. Ion
• C. Isotope
• D. Molecule

Answer: (A)

The idea being tested is how balance between positive and negative charges determines an atom’s charge state. Protons carry positive charge in the nucleus and electrons carry negative charge around it; neutrons are neutral and don’t affect charge. When the number of protons equals the number of electrons, their charges cancel and the atom has no net charge, so it is a neutral atom. If electrons are added or removed, the balance shifts and the atom becomes an ion with a positive or negative net charge. Isotopes differ in the number of neutrons (affecting mass, not charge), and a molecule is simply two or more atoms bonded together, not a single atom’s charge state. So, an atom with equal numbers of positive and negative particles is best described as a neutral atom.