MCQ Detailed View

A molecule is formed when two or more atoms bond together chemically. While most elements exist in molecular form, not all of them have multiple atoms in each molecule. Some elements naturally exist as monoatomic molecules, meaning their molecules consist of a single atom.

Among the given options:

1. 
   

   Helium (He): Helium is a noble gas and belongs to Group 18 of the periodic table. Noble gases are known for their inert nature, meaning they are chemically stable and rarely form bonds with other atoms. Helium atoms exist independently as single atoms because their outermost electron shell is completely filled, making them stable on their own. Therefore, helium is a monoatomic molecule.

   
   


2. 
   

   Ozone (O₃): Ozone consists of three oxygen atoms bonded together, making it a polyatomic molecule.

   
   


3. 
   

   Hydrogen (H₂): Hydrogen naturally occurs as diatomic molecules, meaning two hydrogen atoms bond to form a molecule for greater stability.

   
   


4. 
   

   Nitrogen (N₂): Nitrogen gas is also diatomic, consisting of two nitrogen atoms bonded by a triple bond, forming a stable N₂ molecule.

   
   

Monoatomic molecules are typically found among noble gases, including helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These gases exist as single atoms because they have a complete valence electron shell, making them non-reactive and stable without needing to bond with other atoms.

Thus, the correct answer is Helium, as it naturally exists as a single-atom molecule under normal conditions.

Understanding the difference between monoatomic, diatomic, and polyatomic molecules is an important concept in Chemistry, helping students learn about molecular composition, bonding, and the unique behavior of noble gases compared to other elements.