Question

How valency is determined?

Answer 1

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The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom.

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Answer 2

the number of electrons with in the outer shell of the element determine its valency . to calculate the valency of an elemant or molecule , there are multiple methods...
the valency of an atom is equal to the number of electrons in outer shell if that number is four or less.