Which gas is produced when halogen react with water?

Answer 1

Quite honestly, there is no specific gas. Granted there are some chemical reactions that would create gases with halogens and H2O, but since you're being very vague on the specific halogen, I can't provide a specific answer. Not all halogens have large reactions with water. In fact, the government forces the American water supply to contain Fluorine (a halogen) to improve the dental health of the country.

Answer 2

Hydrogen, here is how it happens with potassium as the metal- 2K (s) + 2H2O (l) -> 2KOH (aq) + H2 (g)

Answer 3

hydrogen gas is given off