The correct answer is D. Nitrogen.
Nitrogen is the most abundant constituent of atmospheric air, accounting for 78.09% of the total volume. It is a colorless, odorless, and tasteless gas that is essential for life. Nitrogen is used in the production of ammonia, fertilizers, and explosives. It is also used in the production of nitric acid, which is used in the production of a variety of chemicals, including plastics, dyes, and pharmaceuticals.
Carbon is the second most abundant constituent of atmospheric air, accounting for 0.04% of the total volume. It is a black, solid element that is found in all living things. Carbon is used in the production of steel, plastics, and other materials. It is also used in the production of carbon dioxide, which is a greenhouse gas that contributes to climate change.
Hydrogen is the third most abundant constituent of atmospheric air, accounting for 0.009% of the total volume. It is a colorless, odorless, and tasteless gas that is the lightest element in the universe. Hydrogen is used in the production of ammonia, fertilizers, and explosives. It is also used in the production of hydrogen fuel cells, which are used to power cars and other vehicles.
Oxygen is the fourth most abundant constituent of atmospheric air, accounting for 20.95% of the total volume. It is a colorless, odorless, and tasteless gas that is essential for life. Oxygen is used in the production of steel, plastics, and other materials. It is also used in the production of oxygen tanks, which are used by firefighters and other emergency personnel.