Answer the following question given this paragraph: 

An ion is an atom or group of bonded atoms that has a positive or negative charge. Ions are formed when an atom gains or loses electrons from its valence shell ( Figure below ). This process causes an imbalance between the number of positively charged protons and negatively charged electrons, so the overall ion will carry a net positive or negative charge.


Q: What is an atom or group of bonded atoms that has a positive or negative charge?

 Choices:

- an photon

- an electron

- a neutron

- an ion

A:
an ion
