This question is incomplete because the options are missing; here is the missing section:
How might the destruction of rainforests affect the balance of gases in Earth's atmosphere?
by increasing carbon dioxide and decreasing oxygen
by increasing carbon dioxide and increasing oxygen
by decreasing carbon dioxide and increasing oxygen
by decreasing carbon dioxide and decreasing oxygen
The answer to this question is by increasing carbon dioxide and decreasing oxygen.
Explanation:
Rainforests have a vital role on Earth because these regulate the levels of oxygen vs carbon dioxide. This is because plants including trees, grasses, shrubs, etc. require carbon dioxide as part of the photosynthesis process, and they release oxygen at the end of the process. In this way, rainforests reduce the amount of carbon dioxide and increase oxygen.
In this context, deforestation or the destruction of rainforest for mining, roads, etc. implies there are fewer plants, and therefore, less carbon dioxide is being used and less oxygen is released. This causes an increase in carbon dioxide and a decrease in oxygen.