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Answered Oct 01, 2017
It's supposed to be 2, not 3.The third element is Lithium.
Answered Aug 20, 2017
Isnt it suposed to be 2 not 3, te periodic say hydrogen, helium, Luitithium.
Answered Apr 03, 2017
Answered Mar 07, 2017
Answered Feb 19, 2017
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