Which statement about the periodic table is correct?

A.     The elements with atomic numbers 8, 16 and 34 have the same number of main energy levels.

B.     The elements with atomic numbers 8, 9 and 10 have similar chemical properties.

C.     The elements with atomic numbers 20, 21 and 22 are in the same group.

D.     The elements with atomic numbers 20, 38 and 56 have the same number of electrons in their outer energy level.

D