An ion is an atom that has which of the following characteristics?

• A. It has gained or lost one or more protons, changing it into a different element.
• B. It has gained or lost one or more electrons, giving it a net electric charge.
• C. It has undergone a chemical reaction that changes its number of neutrons.
• D. It has an equal number of protons and electrons, making it electrically neutral.

Answer: (B)

Verified step by step guidance

1. Recall the definition of an ion: an ion is an atom or molecule that has a net electric charge due to the loss or gain of electrons.
2. Understand that protons define the element itself, so changing the number of protons would change the element, which is not what happens when forming an ion.
3. Recognize that neutrons affect the isotope of an element but do not affect the charge, so changing neutrons does not create an ion.
4. Note that an atom with equal numbers of protons and electrons is electrically neutral, so it is not an ion.
5. Therefore, the key characteristic of an ion is that it has gained or lost one or more electrons, resulting in a net positive or negative charge.