Question

Why valency of H is +1 and He is zero?

Answer 1

because hydrogen has one electron and Helium has two electron in first shell.
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Answer 2

valency is the no. of outermost electons or 8- no. of outermost electons and u can also say that the configuration by which an element attains stable noble gas configuration so acc to q thevalency of H will be 1 and that of He is 0 as it does not need any electron it is already a noble gas and is stable!!
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