How much percentage of oxygen is present in the atmosphere?

21%

The correct answer is option 4. 21%.

The Earth's atmosphere is composed of a mixture of gases, and oxygen makes up a significant portion of this mixture. The approximate composition of the Earth's atmosphere is as follows:

• Nitrogen (N₂): Approximately 78%
• Oxygen (O₂): Approximately 21%
• Argon (Ar): Approximately 0.93%
• Carbon Dioxide (CO₂): Approximately 0.04% (varies)
• Trace Gases (including Neon, Helium, Methane, Krypton, Hydrogen, Xenon, and others):** Approximately 0.03%

So, the concentration of oxygen in the atmosphere is around 21%. This oxygen is essential for the respiration of many organisms, including humans, and plays a crucial role in various atmospheric and biological processes.