Which two types of particles are present in equal numbers in an atom, but not in an ion? A. protons and electrons B. protons and neutrons C. inner-shell electrons and outer-shell electrons D. protons and inner-shell electrons

The correct answer is option A which is protons and electrons.

Explanation: An neutral atom contains equal amount of electron and protons. As electrons have negative charge and protons have positive charge and neutrons, third particles in atom are neutral. Since in ions, the number of electron and proton is not equal, thus giving a positive or negative charge.

An atom consists of a central nucleus with contains positively charged particles called protons and uncharged particles called neutrons. Negatively charged particles called electrons revolve around the central nucleus along specific orbitals. In a neutral atom, the number of positive protons and negative electrons is same. A metal atom has the tendency to lose electrons from its outermost electronic shell (orbital) to form a positive ion (cation). As a result, the number of electrons decreases. On the other hand, a non-metal atom has the tendency to gain electrons to form a negative ion (anion). As a result, the number of electrons increases. Therefore, electrons and protons are the two types of particles that are present in equal numbers in an atom but not in an ion.

(Answer) (A) protons and electrons