What is the composition of a small part of Venus's atmosphere?

The atmosphere of Venus is primarily composed of carbon dioxide, which makes up about 96.5% of its atmosphere. The presence of nitrogen follows, constituting around 3.5%. This unique combination creates an extremely dense atmosphere that traps heat through the greenhouse effect, leading to the planet's high surface temperatures. The dominance of carbon dioxide is significant in understanding Venus's climatic conditions, pressure levels, and the potential for studying greenhouse gases.

In this context, while helium and neon do exist in trace amounts in various planetary atmospheres, they are not major components of Venus's atmosphere. Hydrogen and oxygen are also not present in significant concentrations on Venus, as they are more commonly associated with Earth. Similarly, while water does exist as vapor, it is not a primary component of Venus's atmosphere; the gases in option C do not accurately reflect the main constituents found in the atmospheric analysis of Venus. Thus, carbon dioxide and nitrogen is the correct choice, as it accurately depicts the substantial makeup of Venus's atmosphere.