There are a lot of gases that can be found in the planet Venus's atmosphere that truly makes it one of the planets that people cannot live in. First of all, more than 90% of the atmosphere is composed of carbon dioxide which is the type of gas that we breathe out.
Venus does not have any plants that can convert the carbon dioxide to oxygen. The rest of the gases that can be found are nitrogen and sulfur dioxide. Do take note that it also has clouds that are made up of sulfuric acid. The greenhouses gases on this planet are so strong that it has caused the oceans to dry up.