An atom that has lost or gained one or more electrons and therefore carries a net electric charge is called what?

Introduction / Context:
Atoms are normally neutral because they contain equal numbers of protons and electrons. However, in many chemical processes, atoms can lose or gain electrons. When this happens, the balance of charge is disturbed, and the species becomes electrically charged. This question asks for the correct term used to describe such charged species. Knowing this definition is fundamental in chemistry, since ions play key roles in solutions, solids and biological systems.

Given Data / Assumptions:

• We are dealing with atoms that lose or gain electrons.
• Gaining electrons leads to an excess of negative charges.
• Losing electrons leads to an excess of positive charges.
• The options include proton, ion, isotope, neutron and molecule.

Concept / Approach:
The term ion is defined as any atom or group of atoms that has a net electric charge due to the loss or gain of one or more electrons. A positively charged ion is called a cation, while a negatively charged ion is called an anion. Protons and neutrons are subatomic particles inside the nucleus, and isotopes refer to atoms of the same element with different numbers of neutrons. A molecule is a neutral group of atoms bonded together. The correct term for a charged atom is therefore ion.

Step-by-Step Solution:
Step 1: Consider an atom that is neutral when it has equal numbers of protons and electrons. Step 2: If the atom loses electrons, it has more protons than electrons and becomes positively charged. Step 3: If the atom gains electrons, it has more electrons than protons and becomes negatively charged. Step 4: The general name for any charged atom or group of atoms formed in this way is ion. Step 5: Therefore, the correct term to describe an atom that has lost or gained electrons is ion.

Verification / Alternative check:
Examples from everyday chemistry confirm this usage. In sodium chloride, NaCl, sodium atoms lose one electron to become Na⁺ cations and chlorine atoms gain one electron to become Cl⁻ anions. In electrolytes dissolved in water, such as Na⁺, K⁺, Ca²⁺ and Cl⁻, the charged species are called ions. Textbooks define cations and anions as types of ions. None of these examples uses the words proton or isotope to describe the charged species, which further confirms ion as the standard term.

Why Other Options Are Wrong:
Option A, proton, refers to a positively charged subatomic particle in the nucleus, not the whole atom. Option C, isotope, describes atoms of the same element with different neutron counts, but they may be neutral or charged; the term does not specifically refer to charge. Option D, neutron, is a neutral subatomic particle and does not mean a charged atom. Option E, molecule, is a neutral combination of atoms bonded together and is not defined by net charge. Only option B, ion, is the correct term for an atom that has lost or gained electrons and now carries a net charge.

Common Pitfalls:
Some learners mix up the terms ion and isotope because both involve changes in atomic particles, but isotopes differ in neutrons, while ions differ in electrons. Others confuse proton with positive ion, because both are positively charged. To avoid this, remember that a proton is a single particle, whereas an ion is an entire atom or group of atoms with a net charge. Keeping these definitions clear is essential for understanding acid base chemistry, redox reactions and electrochemistry.

Final Answer:
An atom that has lost or gained electrons and now carries a net positive or negative charge is called an Ion.