What is the definition of ionisation?

Ionisation refers to the process through which an atom loses or gains electrons, resulting in the formation of charged particles known as ions. When an atom loses one or more electrons, it becomes positively charged (a cation), and when it gains electrons, it becomes negatively charged (an anion). This process can occur through various means, such as exposure to radiation, chemical reactions, or thermal energy.

The chosen definition effectively captures the essence of ionisation as it describes the transformation of a neutral atom into charged components, which can be viewed as positive and negative entities. Understanding ionisation is crucial in fields such as chemistry and physics, as it plays a significant role in chemical bonding, electrical conductivity, and reactions involving plasma and other states of matter.

The other options describe processes related to atomic or molecular interactions but do not accurately represent ionisation. For instance, loss of energy from an atom does not necessarily equate to the creation of ions, and the formation of stable atoms from unstable ones pertains to nuclear reactions rather than electron transfer. Similarly, the combining of atoms to form molecules refers to chemical bonding and does not involve the charging of particles that characterises ionisation.