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The correct answer is Argon. Among the noble gases, Argon is the most abundant in Earth’s atmosphere. It makes up about 0.93% by volume, which is far higher than the concentrations of other noble gases. Neon, helium, krypton, and xenon are present only in trace amounts, while radon is radioactive and occurs naturally in very tiny quantities.

Argon is a chemically inert gas belonging to Group 18 of the periodic table. Because of its stable electronic configuration (completely filled outer shell), it does not readily form compounds under normal conditions. This inert property is why argon has many practical applications.

One of the major uses of argon is in industrial processes, such as providing an inert atmosphere for welding and metallurgy, where metals must be protected from oxidation at high temperatures. It is also widely used in incandescent and fluorescent lighting, where it prevents the filament from deteriorating quickly. In laboratories, argon serves as a protective gas in reactions sensitive to oxygen or moisture.

In the atmosphere, argon originates mainly from the radioactive decay of potassium-40 (K-40) present in rocks and minerals. Over geological time, this process has contributed significantly to the accumulation of argon in the air.

The discovery of argon in 1894 by Lord Rayleigh and Sir William Ramsay marked an important step in understanding the noble gases. Its abundance explains why it is more economically feasible to extract and use argon compared to other rare gases.

Thus, argon’s high presence in the atmosphere and its unique inertness make it the most important noble gas in both natural and industrial contexts.