Question

Except ......... gas all other noble gases have octet in their valence shell.

Answer 1

Except helium gas, all otheer noble gases have octate in their valence shell. Helium has an electronic configuration : $1s^2$. Therefore, it does not involve octate in its configuration. It is a colorless, tasteless, odorless, non toxic, monoatomic gas. It has a boiling point, lowest of all the elements.