Question

Which one of the following elements is a noble gas?

• A. Hydrogen
• B. Helium
• C. Lithium
• D. Beryllium

Hint:

Noble gases are chemically inert because their outermost shells are completely filled.

Answer 1

The Correct Option is B

Concept:
Noble gases are elements present in Group 18 of the periodic table. These elements have completely filled outermost electron shells and are chemically very stable. Examples of noble gases are: \[ He,\ Ne,\ Ar,\ Kr,\ Xe,\ Rn \]

Step 1: Identifying the noble gas among the options.
Among the given elements:
• Hydrogen belongs to Group 1.
• Lithium is an alkali metal.
• Beryllium is an alkaline earth metal.
• Helium belongs to Group 18. Thus, helium is the noble gas. \[ \boxed{\text{Helium is a noble gas}} \]

Step 2: Understanding why helium is stable.
Helium has electronic configuration: \[ 1s^2 \] Its outer shell is completely filled. Therefore, helium is chemically inert and highly stable. Hence, the correct option is: \[ \boxed{(2)\ \text{Helium}} \]