WAEC - Chemistry (2009 - No. 9)

Which of the following electronic configurations correctly represents an element in period 3 of the periodic table?
1s2 2s2 2p2
1s2 2s2 2p6
1s2 2s2 2p6 3s2 3p4
1s2 2s2 2p6 3s2 3p6 4s1

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