Question

The elements with atomic numbers $2,10,18,36,54$ and $86$ are collectively known as:

• A. alkaline earth metals
• B. inert gases
• C. halogens
• D. rare earths

Answer 1

The correct option is B inert gases

Zero group of Mendeleev's periodic table or the group $18$ of long form of periodic table is comprised of six elements and these eleements are called as inert gases as trhese elements do not react (inert) with other elements due to their octet outer electronic configaration which is stable configaration. The electronic configuration is listed in the following table.

S.No	Element	Symbol	Atomic number	Electronic configuration
1	Helium	He	2	1s2
2	Neon	Ne	10	[He] 2s2sp6
3	Argon	Ar	18	[Ne] 3s23p6
4	Krypton	Kr	36	[Ar] 3d104s24p6
5	Xenon	Xe	54	[Kr] 4d105s25p6
6	Radon	Rn	86	[Xe] 4f145d106s26p6