The lightest gas is :

• A. nitrogen
• B. helium
• C. oxygen
• D. hydrogen

The lightest gas among the options provided is D. hydrogen. To understand why hydrogen is the lightest, let's delve into the properties of these gases and their molecular weights.

Understanding Gas Properties

Gases are made up of molecules, and the weight of these molecules determines how "light" or "heavy" a gas is. The molecular weight is a crucial factor in comparing different gases. Here’s a quick overview of the molecular weights of the gases listed:

• Nitrogen (N₂): Approximately 28 g/mol
• Helium (He): Approximately 4 g/mol
• Oxygen (O₂): Approximately 32 g/mol
• Hydrogen (H₂): Approximately 2 g/mol

Why Hydrogen is the Lightest

From the molecular weights listed, hydrogen has the lowest molecular weight at about 2 g/mol. This means that hydrogen molecules are lighter than those of nitrogen, helium, and oxygen. To put this into perspective, if you were to fill balloons with each of these gases, the hydrogen-filled balloon would rise the highest because it is less dense than the surrounding air.

Real-World Applications

Hydrogen's lightness has practical implications. For instance, it was historically used in airships and balloons. Although helium is now preferred due to its non-flammable nature, hydrogen's low density makes it an excellent candidate for lifting applications.

Comparative Analysis

Let’s compare hydrogen with helium, the second lightest gas on the list. Helium, while also light, has a molecular weight of about 4 g/mol, which is still double that of hydrogen. This difference in molecular weight is significant when considering buoyancy and lift.

Conclusion

In summary, hydrogen is the lightest gas among the options given, with a molecular weight of 2 g/mol. This characteristic not only makes it the lightest but also gives it unique properties that have been utilized in various applications throughout history. Understanding these properties helps us appreciate the role of different gases in science and industry.