Which option answers this correctly: what is the main gas in Earth’s atmosphere?

Sheeraz Ahmed graduated from National University of Modern Languages Islamabad in 2019, currently he is CSS Aspirant, and he also appeared in Sindh Public Service Commission (SPSC), Federal Public Service Commission (FPSC) for the purpose of recruitment. At our site Sheeraz publishes the Important MCQs to help students and Job Seekers.