When a pot of water has been boiling vigorously for several minutes, the bubbles that emerge from the liquid water are composed of
1. air
2. water vapor
3. h2 gas and o2 gas in a 1: 1 ratio
4. h2 gas and o2 gas in a 2: 1 ratio

Well, water is composed H2 gas and O2 gas in a 2:1 ratio, and the bubbles that form at the bottom of the pan is just the water changing from a liquid to a gas, and im pretty sure its water vapor that comes out of the pan. I hope that helped??? :)