Final answer:
NaCl is mischaracterized as a molecule because it is an ionic compound with a crystal lattice structure and is held together by ionic bonds. Molecules are distinct entities formed by covalent bonds, which is not the case for NaCl.
Step-by-step explanation:
Understanding Ionic Compounds and NaCl
It is incorrect to speak of a molecule of solid NaCl for option a: Because NaCl is an ionic compound, not a molecule. A molecule is a group of atoms bonded together through covalent bonds, sharing electrons. In contrast, NaCl is composed of sodium (Na) ions and chloride (Cl) ions held together by ionic bonds, which are electrical attractions between positively and negatively charged ions. NaCl forms a crystalline structure where each ion is surrounded by ions of opposite charge, repeating throughout the material.
NaCl's crystal lattice structure means that it does not exist as a discrete molecule. Instead, it has an extensive three-dimensional network of ions in a repeating pattern. The formula NaCl indicates the ratio of sodium ions to chloride ions, which is 1:1, but does not imply that they exist as discrete molecules.
Moreover, NaCl has a high melting point, characteristic of ionic compounds, and is quite different from covalent molecules like water (H2O). These ionic properties are crucial for understanding why we cannot accurately describe NaCl in terms of molecules.