Arrange the following trace gases in correct sequence of their concentration in atmosphere in descending order: (A)M ethane (B) Krypton (C) Helium (D) Neon (E) Hydrogen Choose the correct answer from the options given below:
Understanding Atmospheric Trace Gas Concentrations
The Earth's atmosphere is primarily composed of Nitrogen (about 78%) and Oxygen (about 21%). The remaining 1% consists of various other gases, which are often referred to as trace gases. These include Noble gases like Argon, Neon, Helium, Krypton, and Xenon, as well as other gases like Carbon Dioxide, Methane, Hydrogen, Nitrous Oxide, Ozone, etc. The question asks us to arrange five specific trace gases based on their concentration in the atmosphere in descending order (from highest concentration to lowest concentration).
Atmospheric Concentrations of Specified Trace Gases
Let's look at the approximate concentrations of the trace gases listed in the question:
- (A) Methane (CH₄): Approximately 1.9 parts per million (ppm)
- (B) Krypton (Kr): Approximately 1.1 parts per million (ppm)
- (C) Helium (He): Approximately 5.2 parts per million (ppm)
- (D) Neon (Ne): Approximately 18.2 parts per million (ppm)
- (E) Hydrogen (H₂): Approximately 0.55 parts per million (ppm)
Note: Concentrations, especially for gases like Methane, can vary slightly depending on location and time due to human activities and natural processes.
Arranging Gases by Concentration (Descending Order)
To arrange the gases in descending order of concentration, we compare their approximate ppm values:
\(18.2 \text{ ppm (Neon)} > 5.2 \text{ ppm (Helium)} > 1.9 \text{ ppm (Methane)} > 1.1 \text{ ppm (Krypton)} > 0.55 \text{ ppm (Hydrogen)}\)
Mapping these concentrations back to the letters (A) to (E) assigned in the question:
- Neon (D) has the highest concentration (\(\approx\) 18.2 ppm).
- Helium (C) has the second highest concentration (\(\approx\) 5.2 ppm).
- Methane (A) has the third highest concentration (\(\approx\) 1.9 ppm).
- Krypton (B) has the fourth highest concentration (\(\approx\) 1.1 ppm).
- Hydrogen (E) has the lowest concentration among these (\(\approx\) 0.55 ppm).
Therefore, the correct sequence in descending order of concentration is (D), (C), (A), (B), (E).
Comparing with Options
Let's compare our derived sequence (D), (C), (A), (B), (E) with the given options.
- Option 1: (E), (B), (D), (A), (C) - Incorrect
- Option 2: (D), (B), (E), (A), (C) - Incorrect
- Option 3: (D), (C), (A), (B), (E) - Correct
- Option 4: (D), (E), (B), (A), (C) - Incorrect
The sequence (D), (C), (A), (B), (E) correctly represents the trace gases Neon, Helium, Methane, Krypton, and Hydrogen arranged from highest to lowest concentration in the atmosphere.
| Gas | Symbol | Letter Code | Approximate Concentration (ppm) | Rank (Descending Order) |
|---|---|---|---|---|
| Neon | Ne | (D) | 18.2 | 1 |
| Helium | He | (C) | 5.2 | 2 |
| Methane | CH₄ | (A) | 1.9 | 3 |
| Krypton | Kr | (B) | 1.1 | 4 |
| Hydrogen | H₂ | (E) | 0.55 | 5 |
The final arrangement of the trace gases in descending order of their concentration in the atmosphere is Neon, Helium, Methane, Krypton, Hydrogen, corresponding to the sequence (D), (C), (A), (B), (E).
Revision Table: Atmospheric Gases
| Gas | Approximate Percentage (%) | Approximate Concentration (ppm) |
|---|---|---|
| Nitrogen (N₂) | 78.08% | 780,840 |
| Oxygen (O₂) | 20.95% | 209,500 |
| Argon (Ar) | 0.93% | 9,340 |
| Carbon Dioxide (CO₂) | 0.04% | 415 (varies, increasing) |
| Neon (Ne) | 0.00182% | 18.2 |
| Helium (He) | 0.00052% | 5.2 |
| Krypton (Kr) | 0.00011% | 1.1 |
| Methane (CH₄) | ~0.00019% | ~1.9 (varies, increasing) |
| Hydrogen (H₂) | ~0.000055% | ~0.55 |
Additional Information: Trace Gases and Their Importance
Trace gases, despite their low concentrations, play crucial roles in the Earth's climate system and atmospheric chemistry.
- Methane (CH₄): A potent greenhouse gas, second only to carbon dioxide in its contribution to global warming from anthropogenic emissions. It is produced from natural sources like wetlands and human activities like agriculture, fossil fuel production, and waste decomposition.
- Krypton (Kr), Helium (He), Neon (Ne): These are noble gases and are chemically inert. They do not significantly participate in atmospheric chemical reactions or directly influence climate. Their concentrations are relatively stable over time, primarily originating from the Earth's crust and radioactive decay (Helium, Krypton). Neon is a product of nucleosynthesis in stars.
- Hydrogen (H₂): The lightest molecule. It has various sources, including biological processes and industrial activities. While its concentration is low, it plays a role in atmospheric chemistry, particularly in reactions involving the hydroxyl radical (OH), which affects the lifetime of other trace gases like methane.
- Greenhouse Gases: Some trace gases, like Methane and Carbon Dioxide, absorb and re-emit infrared radiation, trapping heat in the atmosphere. These are known as greenhouse gases and are essential for maintaining a habitable temperature on Earth, but increased concentrations due to human activities are causing global warming.
Understanding the relative abundance of these trace gases is fundamental to atmospheric science and environmental studies.
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