Question

What is the correct order of occurrence (\% by weight) in air of \(\mathrm{Ne}, \mathrm{Ar}, \mathrm{Kr} ?\) (a) \(\mathrm{Ne}>\mathrm{Ar}>\mathrm{Kr}\) (b) \(\mathrm{Ar}>\mathrm{Ne}>\mathrm{Kr}\) (c) \(\mathrm{Ar}>\mathrm{Kr}>\mathrm{Ne}\) (d) \(\mathrm{Ne}>\mathrm{Kr}<\mathrm{Ar}\)

Short answer

The correct order is (b) \(\mathrm{Ar} > \mathrm{Ne} > \mathrm{Kr}\).

Step-by-step solution

Understanding the Composition of Air

Air primarily consists of nitrogen and oxygen, but also contains small amounts of other gases. The noble gases such as neon (\(\mathrm{Ne}\)), argon (\(\mathrm{Ar}\)), and krypton (\(\mathrm{Kr}\)) are present in trace amounts. We need to establish the relative abundance of these gases in air.

Finding the Abundance of Argon

Argon is one of the more abundant noble gases in the Earth's atmosphere. It constitutes approximately 0.93% by volume of dry air, making it the most abundant noble gas.

Examining the Abundance of Neon

Neon is less abundant than argon. It occupies a smaller fraction of the air, with a volume percentage of about 0.0018%.

Analyzing the Abundance of Krypton

Krypton is even less abundant in the atmosphere compared to neon and argon. It has a fractional volume of approximately 0.0001%.

Arranging in Order of Decreasing Abundance

Based on the percentages of volume in air: Argon is the most abundant, followed by neon, and krypton is the least abundant. Therefore, the correct order by weight in air is \(\mathrm{Ar} > \mathrm{Ne} > \mathrm{Kr}\).

Key concepts

Composition of Air

Air is all around us, but have you ever wondered what it's made of? The air we breathe is a mixture of gases. The two main components are nitrogen and oxygen. Nitrogen makes up around 78% of air, while oxygen contributes about 21%. These are the gases that sustain life.
But there's more to air than just these two. There are also trace amounts of other gases. Among these are the noble gases, which make up a tiny fraction of the atmosphere. These include neon, argon, and krypton, among others. While not abundant, these gases serve various important roles.
The noble gases are unique because they don't react easily with other substances. This makes them incredibly stable and useful in various applications, from lighting to scientific research.

Argon Abundance

Argon is quite special among the noble gases present in the air because it is the most abundant. Although it only makes up about 0.93% of the atmosphere, this is significant when compared to other noble gases.
• Argon's abundance in the air has practical benefits. Its stability makes it perfect for preserving historical documents and protecting reactive elements. If you ever see an exhibit in a museum sealed in glass, argon might be playing a part in preserving it.
• It's often used in light bulbs and arc welding due to its inert nature. Argon doesn't interact with a metal's properties while it's being welded.
Even though argon is only a small part of our atmosphere, it plays a big role in various industries, thanks to its inert qualities and relative abundance.

Neon Abundance

Neon is another noble gas found in our atmosphere, albeit in smaller quantities than argon. Neon represents about 0.0018% by volume of air. This may seem like a tiny amount, but neon has some fascinating uses.
• Perhaps the most famous use of neon is in neon signs. These are vibrant, glowing signs you might see in cityscapes, designed to stand out at night.
• Neon lights emit a distinct reddish-orange glow, although with the help of other gases, they can appear in many different colors.
It's amazing to think that such a small amount of gas can have such a visible impact in our daily lives. Despite its minimal presence in the atmosphere, the use of neon is widespread in advertising, art, and technology.

Krypton Abundance

Krypton is one of the rarest noble gases in the air, with a volume fraction of about 0.0001%. While it may be invisible to the naked eye, krypton has its own set of unique properties and applications.
• Krypton gas is often used in lighting, similar to its noble gas cousins. However, its applications are a bit more specialized. Krypton is found in certain high-intensity lamps and fluorescent lights, especially in photography lighting for its brilliant white light.
• Another interesting use of krypton is in the field of science. Krypton is used in certain isotopic applications, including in some types of radioactive tracing and photon propulsion.
Krypton is less prevalent but stands out with its specialized uses. It's another example of how even the smallest components of air can have big applications.