The lightest gas on Earth is:

• A. Hydrogen
• B. Oxygen
• C. Helium
• D. Chlorine

The lightest gas on Earth is Hydrogen. It is the simplest and most abundant element in the universe, consisting of just one proton and one electron. This makes it much lighter than other gases like oxygen, helium, or chlorine.

Why Hydrogen is the Lightest

Hydrogen's low atomic weight contributes to its status as the lightest gas. Here are some key points:

• Atomic Structure: Hydrogen has an atomic number of 1.
• Density: It has a very low density compared to other gases.
• Applications: Due to its lightness, hydrogen is used in various applications, including fuel cells and balloons.

Comparison with Other Gases

To give you a clearer picture, here’s how hydrogen compares to the other options:

• Oxygen: Heavier than hydrogen, essential for respiration.
• Helium: Also lighter than air but heavier than hydrogen.
• Chlorine: A heavier gas used in disinfectants.

In summary, hydrogen is the lightest gas on Earth, making it unique among the options provided.