The correct answer is A. Nitrogen.
Nitrogen is the most abundant element in the Earth’s atmosphere, making up about 78% of the air we breathe. It is an odorless, colorless, and tasteless gas that is essential for life. Nitrogen is used by plants to create proteins and other essential molecules, and it is also used by animals to breathe.
Carbon dioxide is the second most abundant gas in the atmosphere, making up about 21% of the air we breathe. It is a colorless, odorless gas that is produced when plants and animals breathe. Carbon dioxide is also released into the atmosphere when fossil fuels are burned.
Oxygen is the third most abundant gas in the atmosphere, making up about 21% of the air we breathe. It is a colorless, odorless, and tasteless gas that is essential for life. Oxygen is used by plants and animals to breathe, and it is also used in combustion reactions.
Hydrogen is the most abundant element in the universe, but it is only a very small fraction of the Earth’s atmosphere, making up about 0.00005% of the air we breathe. It is a colorless, odorless, and tasteless gas that is highly flammable.