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A)  1s2 2s2  2p6   3s2   :  Z = 12 
      it is a metal in group 2:  period 3..       magnesium, 

b)  1s2  2s2  2sp6  3s1  :  Z = 11
     it is an alkali metal....    it is Sodium  in group 1.. in period 3..

c)  2, 8,  7
     1s2  2s2  2p6  3s2  3p 5  :  Z  =17          period 3..  group  17.
      it is a halogen.. next to noble gas config...  it is chlorine.

d)  1s2  2s1
           group 1,,,  period 2.  alkali metal.. Lithium...

1 5 1
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