Answer : The correct option is, Electron.
Explanation :
There are three subatomic particles of an atom which are electrons, protons and neutrons. The protons are positively charged, the electrons are negatively charged and neutrons are neutral (no charge).
A neutral atom is an atom that has same number of electrons and protons. When a neutral atom gain an electron, it becomes a negatively charged ion. When a neutral atom lose an electron, it becomes a positively charged ion. That means the atom change when the electron is lost or gained.
Hence, if the atom undergoes a change and becomes a positive ion, in this process the lost subatomic particle is electron.
