Which of the following is true of anions?

Anions are negatively charged ions that form when an atom gains one or more electrons. The process involves the transfer of electrons from one atom to another, resulting in a surplus of negatively charged particles relative to the number of positively charged protons in the nucleus. This gain of electrons is what gives anions their negative charge.

The incorrect choices highlight common misconceptions. For instance, anions can exist in various states of matter—solid, liquid, or gas—so the notion that they can only occur in gaseous states is inaccurate. Additionally, gaining protons would actually increase the positive charge of an atom, not create an anion. Lastly, anions, by definition, are not positively charged; they specifically carry a negative charge due to the electron gain. Thus, the formation of anions through the transfer of electrons is a fundamental concept in understanding ionic bonding and chemical reactivity.