Group 18 consists of elements: helium, neon, argon, krypton, xenon, radon and oganesson. All these are gases and chemically unreactive. They form very few compounds, because of this they are termed as noble gases. All noble gases have general electronic configuration ns²np⁶ except helium which has 1s². Many of the properties of noble gases including their inactive nature are ascribed to their closed shell structures. Due to stable electronic configuration these gases exhibit very high ionization enthalpy. However, it decreases down the group with increase in atomic size. Atomic radii increase down the group with increase in atomic number. Since noble gases have stable electronic configurations, they have no tendency to accept the electron and therefore, have large positive values of electron gain enthalpy.

Which of the following is the second most abundant noble gas in the atmosphere?

Neon

The correct answer is option 3. Neon.

Let us go into more detail about the noble gases and their abundances in the Earth's atmosphere. The noble gases in the Earth's atmosphere include Argon (Ar), Neon (Ne), Helium (He), Krypton (Kr), and Xenon (Xe). Here’s a detailed look at their relative abundances:

1. Helium (He)

Abundance: Approximately 5.24 ppm by volume.

Helium is the third most abundant noble gas. It is produced by the radioactive decay of elements like uranium and thorium. Despite being light and escaping Earth's gravity into space, it remains the third most abundant noble gas due to continuous production and release from the Earth's crust.

2. Argon (Ar)

Abundance: Approximately 0.93% of the atmosphere by volume.

Argon is by far the most abundant noble gas in the atmosphere. It primarily exists as Argon-40, which is produced by the radioactive decay of Potassium-40 in the Earth's crust. Due to its inert nature and substantial production, argon accumulates in the atmosphere.

3. Neon (Ne)

Abundance: Approximately 18 parts per million (ppm) by volume.

Neon is the second most abundant noble gas. It is relatively rare compared to argon but still more abundant than helium and other noble gases. Neon is primarily sourced from the Earth's mantle and is released through volcanic activity.

4. Krypton (Kr)

Abundance: Approximately 1.14 ppm by volume.

Krypton is much less abundant than argon, neon, and helium. It is produced through the decay of various radioactive isotopes and is released into the atmosphere in small quantities.

Neon’s relative abundance comes from its formation and release processes. Although it is much less abundant than argon, it is significantly more abundant than helium, krypton, and xenon. Neon is created in stars through the fusion process and is present in the primordial material from which the Earth was formed. It is released from the Earth’s mantle through volcanic and tectonic activity. This constant release helps maintain its presence in the atmosphere despite its low overall concentration. In contrast, helium, while also produced continuously, is lighter and can escape the Earth's gravitational pull into space, which limits its atmospheric concentration. Krypton and xenon are even less abundant due to their production rates and heavier atomic masses, which mean they are not produced or released in significant amounts compared to neon and argon.

The abundances of noble gases in the Earth's atmosphere are determined by their production mechanisms and physical properties. Argon is the most abundant due to its significant production from radioactive decay. Neon, though much less abundant than argon, is the second most abundant noble gas due to its formation in the Earth's mantle and release through volcanic activity. Helium follows as the third most abundant due to continuous production but limited by its tendency to escape into space. Krypton and xenon are present in even smaller quantities.

Therefore, the second most abundant noble gas in the Earth's atmosphere is Neon.