I can see that the answer to the question "Most of the concentration of which gas results from the activity of producer organisms?" is:
- carbon dioxide
Producer organisms, like plants during photosynthesis, take in carbon dioxide from the atmosphere and convert it into oxygen as a byproduct. This process increases the concentration of oxygen in the atmosphere. So, the activity of producer organisms leads to a decrease in the concentration of carbon dioxide and an increase in the concentration of oxygen in the environment.
