Answers

2016-02-25T22:24:10+05:30
Elements with same valencies are arranged in the same group not period......elements with same no of shells are arranged in the same period...
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2016-02-25T22:54:08+05:30
This is because they have different number of shells.The periods depend on number of shells and not valency or valence electrons.both of them have same number of ve so they are placed in the same group not period.
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