What particle is involved in ionisation?

Ionisation occurs when an atom or molecule gains or loses electrons, resulting in a charged particle, known as an ion. In this process, electrons can be removed from their parent atom or added to it, which alters the overall charge.

Electrons are subatomic particles that carry a negative charge and are found in the outer regions of an atom. When an electron is removed from an atom, that atom becomes positively charged, and when an electron is added, it becomes negatively charged. This ability of electrons to be transferred between atoms is fundamental to the process of ionisation.

In the context of the other options, neutrons and protons do not participate in ionisation as they are located in the atomic nucleus and do not readily interact with the electron cloud surrounding the nucleus. Alpha particles, which are made up of two protons and two neutrons, can cause ionisation in matter, but they do so by knocking electrons off atoms as they pass through, rather than being the primary particles involved in the ionisation process themselves. Thus, the correct answer is electrons, as they are the fundamental particles directly involved in ionising atoms by gaining or losing from the outer electron cloud.