Question

Why does inert gases placed in Zero group

Answer 1

becz it's last orbital full filled by 8 electron that it not react with other metal

Answer 2

The valence shell of nobel gases are completely filled, they have 8 electrons in outer valence shell so their octet is complete. Atoms with full valence electrons shell are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons so their properties are entirely different from other group elements, hence they are called as nobel gases.