Which pair of atomic numbers belongs to the same group of the long form of the periodic table?

A3 and 12
B12 and 20
C7 and 16
D10 and 11

Answer: B

Z = 12 (Mg) and Z = 20 (Ca) both have two valence electrons in an s orbital and are in group 2. Z = 3 and 12 are a diagonal pair, 7 is group 15 and 16 is group 16, and 10 is group 18 while 11 is group 1.

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