Which is the commonest gas in the atmosphere?

Options

A. hellium
B. Nitrogen
C. Ammonia
D. Hydrogen

Explanation

To determine the commonest gas in the atmosphere, we can follow these steps:

### Step 1: Identify the options given in the question.
- Option A: Helium
- Option B: Nitrogen
- Option C: Ammonia
- Option D: Hydrogen

### Step 2: Understand the composition of the atmosphere.
The atmosphere is composed of various gases, and we need to know their approximate percentages to identify the most abundant one.

### Step 3: Analyze the composition.
- Nitrogen (N₂) constitutes about 78% of the atmosphere.
- Oxygen (O₂) makes up about 21%.
- Argon (Ar) is around 0.9%.
- Other gases, including carbon dioxide, neon, and helium, are present in trace amounts.

### Step 4: Compare the options with the atmospheric composition.
From the analysis:
- Helium is not abundant in the atmosphere.
- Ammonia is also not a significant component.
- Hydrogen is present in very small amounts.
- Nitrogen is the most abundant gas.

### Step 5: Conclude the answer.
Based on the information gathered, the commonest gas in the atmosphere is **Nitrogen** (Option B).

### Final Answer:
**Nitrogen (Option B) is the commonest gas in the atmosphere.**

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