Which statement about burning fossil fuels and atmospheric gases is correct?

• A. M methane (CH4) increases solely from agriculture, not fossil fuels.
• B. Oxygen decreases significantly due to combustion.
• C. Carbon dioxide (CO2) is released from carbon stored in fuels, increasing atmospheric CO2.
• D. Nitrous oxide is converted to nitrogen gas.

Answer: (C)

When fossil fuels burn, the carbon stored in them is oxidized to carbon dioxide. The basic reaction is carbon in the fuel plus oxygen from the air forming CO2 (often with water as a second product). This adds more CO2 to the atmosphere, which is why atmospheric CO2 levels rise as we use more fossil fuels.

The other statements don’t fit as well. Methane does come from fossil-fuel processes as well as agriculture, so it’s not solely from agriculture. Oxygen is consumed in combustion, but the atmosphere’s total oxygen amount is so large that global drops are tiny. Nitrous oxide is not simply converted to nitrogen gas in ordinary atmospheric conditions, so that statement isn’t correct.