Halogen is a gas, so your question doesn't make much sense.
If you're asking about a halogen (light) bulb, then the answer is: mainly halogen.
Halogen gas is in a Tungsten-Halogen Light Bulb.
Iodine is the halogen that sublimes directly from a solid to a gas at standard pressure and temperature.
No, it is a noble gas
Noble gases are, for all intents and purposes, unreactive - there are a few noble gas compounds but you have to really work at it to convince noble gases to form bonds. Fluorine is an extremely reactive gas, hence it is not a noble gas. It is a halogen - the most reactive halogen of them all.
Fluorine, at 19 atomic mass units, is the only halogen gas that fits that requirement.
Halogen
Halogen gas is in a Tungsten-Halogen Light Bulb.
Halogen.
Argon is a noble gas. It is not a halogen. Fluorine is a example for that.
The purpose of halogen gas in a tungsten-halogen lamp is to increase the lifespan and efficiency of the lamp. The halogen gas helps to recycle evaporated tungsten back onto the filament, preventing blackening of the glass and extending the life of the lamp.
No halogen gas has a mass of under 15 atomic mass units. The closest is fluorine, at 19.0 atomic mass units.
That'd be Halogen.
Iodine is the halogen that sublimes directly from a solid to a gas at standard pressure and temperature.
No, it is a noble gas
The halogen gas with a mass less than 15 is fluorine (F). It has an atomic mass of approximately 19.00 u, but if considering only the halogen gases, it is the lightest halogen. Fluorine is a pale yellow gas at room temperature and is highly reactive, particularly with alkali and alkaline earth metals.
There are two gases in fluorine(Halogen) family, which are Fluorine and Chlorine. In some cases bromine can also be included as a gas.
Light bulbs are typically filled with an inert gas such as argon or nitrogen, along with a small amount of a halogen gas like bromine or iodine. These gases help to prevent the filament from degrading by reducing evaporation and oxidation.