The lightest, non-inflammable gas is

Options

A. `H_(2)`
B. `He`
C. `N_(2)`
D. Ar

Answer

To solve the question "The lightest, non-inflammable gas is," we will follow these steps:

### Step 1: Identify the lightest gas
- The lightest gas known is hydrogen (H₂), which has a molecular weight of approximately 2 g/mol. However, hydrogen is flammable.

**Hint:** Remember that the lightest gas is determined by its molecular weight.

### Step 2: Determine the next lightest gas
- The next lightest gas after hydrogen is helium (He), which is a monoatomic noble gas with a molecular weight of about 4 g/mol.

**Hint:** Look for gases that are monoatomic and belong to the noble gases category when considering non-inflammable options.

### Step 3: Check for flammability
- Helium is non-inflammable, meaning it does not catch fire or support combustion, making it a suitable candidate for the question.

**Hint:** Non-inflammable gases are typically noble gases, which are known for their chemical inertness.

### Step 4: Evaluate the options
- Compare helium with other gases such as nitrogen and argon. Nitrogen (N₂) has a molecular weight of about 28 g/mol, and argon (Ar) has a molecular weight of about 40 g/mol, both of which are heavier than helium.

**Hint:** Eliminate gases that are heavier than helium when looking for the lightest gas.

### Conclusion
- Therefore, the lightest non-inflammable gas is **helium (He)**.

**Final Answer:** Helium (He)

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