Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain.

Atomic number of helium is 2. Its electronic configuration is K-2. The maximum number of electrons K shell can accommodate is 2. It means that its duplet is complete. Helium atom does not have to gain or lose any electron since, its outermost shell is complete with 2 electrons. Hence, the valency of helium atom is zero.