NOx acid rain source

• A. Vehicles
• B. Plants
• C. Sea spray
• D. Soil microbes

Answer: (A)

When we talk about NOx forming acid rain, the key idea is that nitrogen oxides are produced by combustion processes and then transform in the atmosphere into nitric acid and related compounds that fall with rain. Vehicles are the best illustration because their engines burn fuel at high temperatures and release nitrogen oxides in the exhaust. Those NOx gases react with water vapor and oxygen in the air, driven by sunlight, to form nitric acid and other nitrates, which then dissolve in rain and lower its pH.

Other options don’t contribute NOx to the atmosphere at significant levels. Plants aren’t a major source of NOx; sea spray mainly adds salts rather than nitrogen oxides, and soil microbes do release some nitrogen compounds through soil processes, but not enough NOx to drive acid rain on the scale seen from vehicle emissions.