What element is a Colorless gas nonreactive one of the heaviest glasses?

The element you're describing is likely xenon (Xe). Xenon is a colorless, odorless gas that is part of the noble gases group, known for its lack of reactivity due to having a complete valence electron shell. While it is not typically used in glass, it is one of the heaviest noble gases and can be utilized in specialized applications, such as in certain types of high-intensity lamps and as a general anesthetic.