To determine which element would have a full outer shell of electrons if it gained three electrons, we need to look at the electron configuration of each option:
A. Boron (B): Has 3 electrons in its outer shell (2s² 2p¹). If it gained 3 electrons, it would have 6 in the outer shell, but the outer shell can only hold 8 for stability (full shell).
B. Nitrogen (N): Has 5 electrons in its outer shell (2s² 2p³). If it gained 3 electrons, it would have 8 in the outer shell (which is full).
C. Lithium (Li): Has 1 electron in its outer shell (2s¹). If it gained 3 electrons, it would have 4 in the outer shell, which is not full.
D. Argon (Ar): Already has a full outer shell with 8 electrons (3s² 3p⁶), so gaining electrons would not be applicable.
The correct answer is B. Nitrogen, as gaining three electrons would give it a full outer shell of 8 electrons.
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