Final answer:
Non-flammable, non-toxic gases such as noble gases are characterized by their stability and safety for handling. Helium's non-reactivity is due to its complete electron shell, and noble gases are used in applications that require inert atmospheres or emit light when ionized by electricity.
Step-by-step explanation:
The characteristics of non-flammable, non-toxic gases, especially the noble gases like helium, neon, argon, krypton, xenon, and radon, include being safe to handle due to their lack of reactivity at room temperature and pressure. For example, helium is non-reactive because it has a complete outer shell of electrons, which makes it very stable and unlikely to participate in chemical reactions. Similarly, the other noble gases were believed to be non-reactive for the same reason, although some, like xenon, can react under specific conditions to form compounds such as xenon fluorides. The first compound formed from xenon was prepared in 1962. When an electric current is passed through these gases, like neon or argon, they emit light, which is utilized in signs and lighting.