Answer (score: 0.5): 3. Atoms of which two elements in the ground state have the electron formula of the outer energy level ns^2np^2 1) C 2) Si 3) Mo 4) Ga 5) S

The correct answer is 1) C and 2) Si.<br /><br />The electron configuration $ns^{2}np^{2}$ corresponds to the valence electron configuration of elements in Group 14 (or IV A) of the periodic table. In the ground state, the electron configuration of carbon (C) is $1s^{2}2s^{2}2p^{2}$, and the electron configuration of silicon (Si) is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}$. Both carbon and silicon have the electron configuration $ns^{2}np^{2}$ in their outer energy level.