Question

which gas in earths atmosphere has increased over time due to burning fossil fuels?
oxygen
nitrogen
water vapor
carbon dioxide

Explanation:

Fossil fuels like coal, oil, and gas contain carbon. When burned, they react with oxygen. The chemical reaction \( \text{C + O}_2
ightarrow\text{CO}_2 \) (for pure carbon combustion, simplified as fossil fuels are complex hydrocarbons but main product is \( \text{CO}_2 \)) releases carbon dioxide. Oxygen is consumed in combustion (so its amount doesn't increase due to this process in the context of fossil - fuel burning as a main effect), nitrogen is mostly inert in this combustion process (not produced in significant amounts from fossil - fuel burning to be the answer here), and water vapor (from hydrogen in hydrocarbons reacting \( 2\text{H}_2+\text{O}_2
ightarrow2\text{H}_2\text{O} \)) is a by - product but \( \text{CO}_2 \) has had a more significant and well - documented increase in the atmosphere due to long - term fossil - fuel burning (e.g., from industrial revolution onwards).

Answer:

carbon dioxide