What makes up four-fifths of the air in our atmosphere?

The correct answer is nitrogen. Nitrogen makes up approximately 78% of the Earth's atmosphere, which is a significant portion, or roughly four-fifths. This gas is colorless, odorless, and inert, and it plays a crucial role in the atmosphere by diluting oxygen and helping to maintain pressure at breathable levels for living organisms.

Oxygen, while essential for life and constituting about 21% of the atmosphere, does not dominate the composition like nitrogen does. Carbon dioxide, in contrast, is present in much smaller quantities (around 0.04%) and is vital for processes like photosynthesis but does not constitute four-fifths of the atmospheric composition. Hydrogen is even less abundant and primarily exists in trace amounts. Understanding these proportions is essential not just in the context of cosmetology but also in grasping broader environmental and atmospheric science concepts.