Four elements have been listed, out of which three are alike in some manner and one is different. Select the odd one.

Correct option is A

Concept:
To find the odd one out, we need to analyze the given elements based on their properties, specifically focusing on their position in the periodic table or their chemical characteristics.
Elements:
1. Sodium (Na):
· Sodium is a metal and belongs to Group 1 (alkali metals) in the periodic table.
· It is highly reactive and forms compounds readily.
2. Helium (He):
· Helium is a noble gas, located in Group 18 of the periodic table.
· It is chemically inert (non-reactive).
3. Neon (Ne):
· Neon is also a noble gas, located in Group 18.
· Like helium, it is chemically inert.
4. Argon (Ar):
· Argon is another noble gas, located in Group 18.
· It is also chemically inert.
Solution:
· Helium, Neon, and Argon are all noble gases (Group 18), which are chemically inert and non-reactive.
· Sodium, on the other hand, is an alkali metal (Group 1) and is highly reactive, unlike the noble gases.
Conclusion:
The odd one out is Sodium because it is a reactive metal, whereas the other three (Helium, Neon, and Argon) are noble gases.
Correct Answer:
(a) Sodium.