Answer:
According to the figure, oxygen gas makes up 21 percent of Earth's atmosphere.
Step-by-step explanation:
This figure is called "pie chart", these type of charts are use to show different categories (types, sorting) of a topic represented as slices whose sum is the 100%.
In this case, the chart topic would be "gases of Earth's atmosphere" and the type of gases represented are: oxygen, nitrogen and water vapor.
Analyzing the chart, oxygen gas makes up 21% of Earth's atmosphere, nitrogen gas makes up 78% and the rest is water vapor. The sum of those gases is the 100%.