Ionisation is the process in which an atom or molecule gains or loses electrons, resulting in the formation of charged particles called ions. When an atom loses one or more electrons, it becomes a positively charged ion, known as a cation. Conversely, when an atom gains electrons, it becomes a negatively charged ion, called an anion. This process can occur through various means, such as exposure to radiation, heat, or chemical reactions. Ionisation plays a crucial role in many scientific fields, including chemistry, physics, and biology. For example, in mass spectrometry, ionisation is used to analyze the composition of substances by converting them into ions for detection. Additionally, in plasma physics, ionisation is essential for understanding the behavior of ionized gases, which are found in stars and neon lights.