Which of the following gases is a significant component of Mars's atmosphere?

The correct answer is carbon monoxide, as it is one of the notable components of Mars's atmosphere. Mars has a very thin atmosphere, which is primarily composed of carbon dioxide, making up about 95% of it. However, carbon monoxide is present in smaller amounts, typically around 0.07% of the atmosphere, and plays roles in various chemical reactions occurring on the planet.

Understanding Mars's atmosphere is crucial for assessing past water activity and potential habitability, as well as for planning future missions to the planet. Carbon monoxide's presence can influence the planet's geochemical cycles and is of interest to researchers studying the Martian environment.

The other options do not hold a significant presence in Mars's atmosphere. Neon is found in trace amounts, but it is not a major component. Hydrogen is also present, but it exists in very low concentrations compared to carbon monoxide. Ozone is not a component of the Martian atmosphere; it is more relevant to Earth’s atmospheric chemistry due to its formation from chemical reactions involving oxygen.