Which of the following gas components makes up the majority of Earth’s atmosphere?

The correct answer is nitrogen, which constitutes about 78% of Earth's atmosphere. This predominant presence of nitrogen is crucial for multiple reasons. First, nitrogen is a relatively inert gas, which means it does not readily react with other substances under normal conditions. This stability is significant as it allows for a balanced atmosphere that supports life without excessive chemical reactions that could be harmful.

In addition, nitrogen plays an essential role in the nitrogen cycle, which is vital for the growth of plants and the overall health of ecosystems. It is a key component of amino acids, proteins, and nucleic acids in living organisms. Although oxygen is also important and makes up about 21% of the atmosphere, it is nitrogen's abundance that primarily characterizes the atmospheric composition. Other gases such as carbon dioxide and argon represent much smaller percentages, making them less significant in terms of overall atmospheric composition.