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Ions in an ionic compound typically form an orderly crystal structure primarily because every ion is attracted to ions of opposite charge that surround it—above, below, and to all sides. This attraction leads to a highly ordered arrangement, which maximizes the electrostatic forces between positively and negatively charged ions. The result is a stable crystal lattice structure that minimizes energy, making the formation of the crystal structure thermodynamically favorable.

While the other statements mention relevant properties of ionic compounds (such as the existence of positive and negative charges, conductivity when melted, and the fact that they are solid at room temperature), the core reason for the orderly crystal structure is the attraction between oppositely charged ions.