What is an ion?

• A. An atom with a net electric charge due to gain or loss of electrons
• B. An atom with equal numbers of protons and electrons
• C. An atom that has lost all electrons
• D. An atom with extra neutrons

Answer: (A)

An ion is an atom that has a net electric charge because it has gained or lost electrons. In a neutral atom, protons and electrons balance, giving no overall charge. When electrons are removed, the atom becomes positively charged; when electrons are added, it becomes negatively charged. Losing all electrons would leave a bare nucleus, not a typical ion, and an atom with extra neutrons is an isotope, which changes mass but not charge. So the description matches how ions form and why they carry charge. For example, sodium can lose an electron to become Na+, while chlorine can gain an electron to become Cl-.