Question

{"given":"We need to identify the crystal structure type of NaCl (sodium chloride) crystal from the given options: FCC, BCC, HCP, and simple cubic.","key_observation":"NaCl adopts a face-centered cubic (FCC) structure where the larger Cl⁻ ions form an FCC lattice and the smaller Na⁺ ions occupy the octahedral holes. This arrangement maximizes the electrostatic attraction between oppositely charged ions while minimizing repulsion, making it the most stable structure for NaCl.","option_analysis":[{"label":"(A)","text":"FCC","verdict":"correct","explanation":"This is correct. NaCl has a face-centered cubic structure with Cl⁻ ions at FCC lattice points and Na⁺ ions in octahedral holes, giving a coordination number of 6 for both ions."},{"label":"(B)","text":"BCC","verdict":"incorrect","explanation":"Body-centered cubic is not the structure of NaCl. BCC would give different coordination numbers and packing efficiency than what NaCl actually has."},{"label":"(C)","text":"HCP","verdict":"incorrect","explanation":"Hexagonal close packing is not the structure of NaCl. HCP is more common for metallic crystals and some covalent compounds, not ionic crystals like NaCl."},{"label":"(D)","text":"simple cubic","verdict":"incorrect","explanation":"Simple cubic would have very low packing efficiency and coordination number of 6, but NaCl does not adopt this less stable structure."}],"answer":"(A)","formula_steps":[]}