The most abundant rare gas in the atmosphere is?

1. Analyze the question

The question asks for the most abundant "rare gas" (also known as a noble gas or inert gas) found in the Earth's atmosphere.

2. Explain the concept

Noble gases are elements found in Group 18 of the periodic table. They are characterized by having a full valence shell, which makes them chemically inert (unreactive). While they are called "rare" gases, they exist in varying concentrations in the atmosphere.

The composition of the Earth's atmosphere by volume is approximately:

• Nitrogen ($N_2$): ~78%
• Oxygen ($O_2$): ~21%
• Argon ($Ar$): ~0.93%
• Carbon dioxide ($CO_2$): ~0.04%
• Trace amounts of other noble gases (Neon, Helium, Krypton, Xenon).

3. Show the solution

• Helium (He): Exists in the atmosphere in very small quantities (about 0.0005%).
• Neon (Ne): Exists in even smaller quantities (about 0.0018%).
• Argon (Ar): This is the third most abundant gas in the atmosphere after Nitrogen and Oxygen, with a concentration of approximately 0.93%.
• Xenon (Xe): Exists in trace amounts (about 0.000009%).

Comparing these values, Argon has the highest concentration among all the noble gases in the atmosphere.

4. Identify the answer

Based on the atmospheric composition data, Argon is significantly more abundant than Helium, Neon, or Xenon. Therefore, the correct option is C.

5. Exam Tip

To remember the order of abundance of noble gases in the atmosphere, use the mnemonic: "All Needy He-men Keep X-raying" (Argon > Neon > Helium > Krypton > Xenon). Always remember that Argon is the "odd one out" because it is the only noble gas present in a concentration close to 1%.