The noble gas that does not occur in the atmosphere is
(a) Ra
(b) Kr
(c) He
(d) Ne

Q: Why is Radon not present in the atmosphere?

Radon is a radioactive element with a very short half-life. It is formed by the radioactive decay of heavier elements like Uranium and Radium in the earth's crust, and it decays before it can accumulate in the atmosphere.

Q: Is Radium (Ra) a noble gas?

No, Radium (Ra) is an alkaline earth metal belonging to Group 2 of the periodic table. It is also highly radioactive.

Q: Why is 'Ra' given as an option if it's not a noble gas?

This was a typographical error in the official JEE Main paper. The intended option was 'Rn' (Radon), which is the noble gas absent from the atmosphere.

Q: Which noble gas is most abundant in the atmosphere?

Argon (Ar) is the most abundant noble gas in the Earth's atmosphere, making up about 0.93% of it by volume.

Q: Are all noble gases completely unreactive?

While they are generally inert due to their stable electronic configuration, heavier noble gases like Krypton and Xenon can form compounds with highly electronegative elements like Fluorine and Oxygen under specific conditions.

Question

The noble gas that does not occur in the atmosphere is

Options:

(A) Ra

(B) Kr

(C) He

(D) Ne

Sigma Percentile · Accepted Answer

### The Mystery of the Missing Noble Gas

Have you ever wondered what makes up the air we breathe? While nitrogen and oxygen take up the lion's share, there's a quiet, unreactive family of elements hiding in the background—the noble gases. Helium, Neon, Argon, Krypton, and Xenon are all floating around us right now. But there is one member of this elite Group 18 club that is conspicuously absent from our atmosphere.

Let's dive into this intriguing JEE question that asks us to identify this missing noble gas.

### The Radioactive Outcast: Radon

If we list out the noble gases—$	ext{He, Ne, Ar, Kr, Xe, Rn}$—we find that the first five are present in the Earth's atmosphere in varying trace amounts. Argon, for instance, makes up nearly $1\%$ of the air!

However, the heaviest member, **Radon ($	ext{Rn}$)**, is a different story. Radon is a highly radioactive element. It is formed deep underground from the radioactive decay of heavier elements like Uranium and Radium. Because it has a very short half-life (just about 3.8 days for its most stable isotope), it decays into other elements long before it can accumulate in the atmosphere in any significant amount. Therefore, Radon is the noble gas that does not occur in the atmosphere.

### Spotting the Typo

Now, let's look at the options provided in the question:
(a) $	ext{Ra}$
(b) $	ext{Kr}$
(c) $	ext{He}$
(d) $	ext{Ne}$

Wait a minute! Option (a) is $	ext{Ra}$, which stands for **Radium**. Radium is an alkaline earth metal belonging to Group 2 of the periodic table. It is definitely *not* a noble gas.

This is a classic example of a typographical error in an official exam. The examiners intended to write $	ext{Rn}$ (Radon) but mistakenly printed $	ext{Ra}$ (Radium). Since Krypton, Helium, and Neon are all noble gases present in the atmosphere, the only logical choice—despite the misprint—is option (a).

It's a great reminder that while we must know our concepts thoroughly, we also need to be sharp enough to spot when a question has a slight hiccup!

Animated Solution for Chemistry - s and p-Block Elements: The noble gas that does not occur in the atmosphere is

Select Answer:

Visualized Solution

$Noble Gases in the Atmosphere$

$Analyzing the Options$

The Sigma Insight: Group 18 Elements

The Mystery of the Missing Noble Gas

The Radioactive Outcast

Spotting the Typo

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