Question

helium atom has 2 electrons in its valence shell but its valency is not 2.explain

Answer 1

because k shells maximum eletron is 2...

Answer 2

Since electrons of helium are present in 1s orbital, the orbital gets filled with the two electrons. Such that the first orbit is filled because it's maximum revolving orbital around it is 1 with 2 electrons. Due to it's stability power and completely filled orbit, helium has no valency.