Question

Which set of symbols represents atoms with valence electrons in the same electron shell?
(1) Ba, Br, Bi (3) O, S, Te(2) Sr, Sn, I (4) Mn, Hg, Cu

Answer 1

Answer=2

Sr,Sn, and I have their valance electrons in the same electron shell, we know this because they are in the same period (row) on the periodic table.