When an atom gains an electron, the resulting particle is calleda) a proton. b) an anion. c) a cation. d) an isotope. e) none of the above

B) an anion

Explanation:

During bonding atoms may share electron or give out electron . In the case of electrovalent or ionic bonding, electron(s) is/are transferred from one atom to another . The atom that donate the electron are known as donor atom and the atom that receives the electron are known as receivers.

The atom that donate the electron becomes a cation(positively charged) as it lose it electron(s) while the receiver gains electron to become an anion which is a negatively charge ion.  

An example of such interaction is between a sodium atom and a chlorine atom.  The Na atom lose it electron to become positively charged(cation) while the chlorine atom gains electron to become negatively charged(anion). Both atom bond together losing and gaining electron to fulfill the octet rule.

Na+  +  Cl-   → NaCl

- "the choice that is not an indicator of a chemical change is "state of matter changes". more common than not, chemical reactions produce energy in the form of light or heat. along with energy, they also produce a new substance called the product that could be in any state of matter (solid, gas, or liquid)."