1. The primary gas in the Jovian planets is hydrogen.
2. The primary gas in Mars and Venus is carbon dioxide.
3. If I could visit a planet is would be Mars. I want visit Mars because I think it would be cool to explore the volcano Olympus Mons. Because of how big it is said to be. Especially if it is the size of Ohio and extremely tall. I don't know if it would be possible for me to visit Mars, but I think it would be highly likely because Mars is mostly made of carbon dioxide.