Question

Why are noble gases placed in a separate group ​

Answer 1

$because \: they \: will \: not \: react \: with \: other \: elements \: easily$

Noble Gases are also called as Inert Gases

Answer 2

Answer:

because they are unreactive and hence are placed different from every element. since all elements are somehow reactive but only noble gases (inert gases are unreactive)

hope this helped you :)