JAMB - Chemistry (2015 - No. 38)
The elements that belong to the third period of periodic table are
Li, Be, Al and D
Na, P, O and Cl
B, C, N, and O
Na, Mg, S and Ar
Paliwanag
Na, Mg, S and Ar is the set of elements that belong to third period of the periodic table. Option A,B,C have elements which belong to the other period in the periodic table included in them.