Identifying the Second Most Plentiful Gas in Air

The question asks us to identify which gas is the second most abundant in the Earth's atmosphere from the given options. Understanding the composition of the air we breathe is key to answering this.

Atmospheric Gas Composition Explained

The Earth's atmosphere is primarily composed of a few major gases. Here's a breakdown of the main components:

• Nitrogen ($ \text{N}_2 $): This is the most plentiful gas, making up approximately $ 78\% $ of the air.
• Oxygen ($ \text{O}_2 $): This gas is essential for respiration and constitutes about $ 21\% $ of the atmosphere.
• Argon ($ \text{Ar} $): This inert gas accounts for about $ 0.93\% $ of the air.
• Carbon Dioxide ($ \text{CO}_2 $): Although crucial for the climate, it makes up a much smaller portion, around $ 0.04\% $.
• Other trace gases: Gases like Neon, Helium, Methane, Krypton, Hydrogen, etc., exist in very small quantities.

Based on these percentages, Nitrogen ($ \text{N}_2 $) is the most plentiful gas. Oxygen ($ \text{O}_2 $) is the next most abundant gas, making it the second most plentiful gas in the air.

Therefore, among the choices provided (Carbon dioxide, Hydrogen, Nitrogen, Oxygen), Oxygen is the correct answer as the second most plentiful gas in the Earth's air.