Question

why the noble gases are placed in separate groups....

Answer 1

Because :

*They have stable electronic configuration.

*They are much less reactive.

*They don't react with the other elements in the periodic table.

Answer 2

They are non reactive
They have ns₂np₆ configuration except He ns₂
Having stable configuration they don't react like other metals
They posses completely filled shells
They are also called VIII group elements ,0 group,Inert gases