Question

5. Helium atom has 2 electrons in its valence shell but its valency is not
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Answer 1

Answer:

Valency is the number of electrons an atom requires to attain it's stability.But since helium has already filled its outer shell (shell K).It's valency is zero.

Valence electrons are the number of electrons present in the outer most shell.So, helium has 2 electrons present in its K shell. it's valence electrons are 2.

Do not confuse between valency and valence electrons.