ANS:B - Carbon dioxide

Among the options provided, carbon dioxide (CO2) is the gas primarily responsible for global warming. Carbon dioxide is a greenhouse gas, meaning it absorbs and emits infrared radiation within the thermal infrared range. This property allows it to trap heat in the Earth's atmosphere, contributing to the greenhouse effect and causing global warming. Increased levels of carbon dioxide in the atmosphere, largely due to human activities such as burning fossil fuels (coal, oil, and natural gas), deforestation, and industrial processes, have led to enhanced greenhouse effect and global warming. While carbon monoxide (CO) is also a pollutant and contributes to air pollution, it is not as significant in causing global warming as carbon dioxide. Nitrogen (N2) is a major component of the Earth's atmosphere and is considered inert in terms of greenhouse gas effect. Ozone (O3) is a trace gas in the atmosphere and, depending on its location, can act as both a greenhouse gas and a pollutant. However, its contribution to global warming is relatively small compared to carbon dioxide. Therefore, the correct answer is carbon dioxide (CO2).