Which of the following gaseous molecules is monoatomic ?

Options

A. chlorine
B. helium
C. oxygen
D. nitrogen

Answer

To determine which of the given gaseous molecules is monoatomic, we can analyze each option step by step.

### Step 1: Identify the gaseous molecules
Let's assume the options provided are:
- A) Chlorine (Cl2)
- B) Helium (He)
- C) Oxygen (O2)
- D) Nitrogen (N2)

### Step 2: Analyze each molecule
1. **Chlorine (Cl2)**:
- Chlorine exists as a diatomic molecule, meaning it is composed of two chlorine atoms. Therefore, it is not monoatomic.

2. **Helium (He)**:
- Helium is a noble gas and exists as a single atom in its gaseous state. Thus, it is monoatomic.

3. **Oxygen (O2)**:
- Oxygen also exists as a diatomic molecule, consisting of two oxygen atoms. Hence, it is not monoatomic.

4. **Nitrogen (N2)**:
- Nitrogen exists as a diatomic molecule as well, comprising two nitrogen atoms. Therefore, it is not monoatomic.

### Step 3: Conclusion
From the analysis, we find that:
- Chlorine (Cl2) is diatomic.
- Helium (He) is monoatomic.
- Oxygen (O2) is diatomic.
- Nitrogen (N2) is diatomic.

Thus, the only monoatomic gaseous molecule among the options is **Helium (He)**.

### Final Answer
The correct option is **B) Helium (He)**.

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