When do the number of protons equal the number of electrons in an atom?

The number of protons equals the number of electrons in an atom when the atom is in a neutral state, meaning it has not gained or lost any electrons. This condition signifies that the atom is electrically balanced, with positive charges from protons perfectly countering the negative charges from electrons. This balanced state is often referred to as equilibrium in the context of electrical charge.

In scenarios such as ionization, the atom may lose or gain electrons, resulting in a charged particle known as an ion. When an atom loses an electron, it becomes a cation, which has more protons than electrons, leading to a positive charge. Conversely, if it gains an electron, it turns into an anion, having more electrons than protons resulting in a negative charge.

Option D, which refers to cation formation, is specifically about the process of losing electrons and ultimately results in an imbalance of protons and electrons. Similarly, "proton matching" isn't a standard term in atomic theory, and while it seems to imply a relationship between protons and electrons, it does not accurately depict the state of a neutral atom.

Equilibrium is the correct term to describe the state where the number of protons is equal to the number of electrons, indicating the