Answer:
Group 18 elements 
Noble gases
Step-by-step explanation:
The gases in the last group of the periodic table exist in nature in uncombined state. Due to their nature of passiveness, they are called inert gases.
Other names include the noble gases. They are as follows 
Helium
Neon
Argon
Radon
Xenon 
These elements occur in as mono atomic atoms. Hence, they have an atomicity of 1