Define free electron.

• A. When it is removed from orbit
• B. When it is bound to nucleus
• C. When it gains mass
• D. When it becomes a proton

Answer: (A)

A free electron is an electron that is not bound to an atomic nucleus; it has enough energy to escape the nucleus’ pull and move independently. When it is removed from orbit, the atom is ionized and the electron becomes free to travel through space or under the influence of external fields. The other statements describe situations that do not define a free electron: remaining bound to the nucleus is the opposite of free, gaining mass is not what makes an electron free, and becoming a proton is impossible for an electron.