noble gases are least reactive elements due to their cmplt valence shell. other elements react to get configuration of any noble gas.

The Eighth group or the Noble gases also known as the 0 group elements are the least reactive element that've ever known.
These are less reactive as the last shell of the atom in the element have the octet configuration i.e they have 8 electron in the outer mot shell, except the helium, it has duplet cofiguration i.e, 2 electrons in the outer most shell.
These elements are: Helium, Neon, Argon, Krypton, Xenon, Radon.