Which of the following statements about crystals is false?

Question

BlackTom AI · Accepted Answer

Crystals are built from a periodic repetition of a unit cell, so the statement claiming "most crystals do not consist of repeated unit cells" is false.

1. Relevant knowledge points and concepts
- Crystal: a solid with long-range, ordered arrangement of atoms.  
- Lattice and basis: a crystal structure can be described as a Bravais lattice (an array of points showing translational symmetry) plus a basis (the group of atoms attached to each lattice point).  
- Unit cell: the smallest volume that, when translated through all lattice vectors, reproduces the entire crystal.  
- Periodicity vs. aperiodic order: most crystals are periodic; quasicrystals are ordered but nonperiodic exceptions.

2. Step-by-step reasoning
- By definition, a crystal exhibits translational symmetry: moving the lattice by certain vectors maps the structure onto itself.  
- Translational symmetry means the crystal can be generated by repeating a fundamental motif (the unit cell) across space.  
- Therefore, a correct description of a periodic crystal is "consists of repeated unit cells."  
- The given statement asserts the opposite for most crystals; this contradicts the definition and standard description of crystalline solids.

3. Intermediate steps (logical, not numerical)
- Definition: crystal = lattice + basis → whole structure = repetition of basis via lattice translations.  
- Consequence: repeating unit cell is intrinsic to periodic crystals.  
- Exception note: quasicrystals show long-range order without simple periodic unit-cell repetition, but they are rare; they do not make "most crystals."

4. Why the correct answer is correct
- The correct judgment is that the statement is false because the defining feature of (periodic) crystals is precisely that they consist of repeated unit cells. Saying "most crystals do not consist of repeated unit cells" contradicts that defining property.

5. Why other options would be incorrect (briefly)
- No other answer options were provided in the prompt. For completeness, common true statements about crystals are that they have long-range order, can be anisotropic, and are described by unit cells; any option denying these would be incorrect.

6. Conclusion
- The provided statement is false; this explanation confirms the given answer: "Although made of a regular arrangement of atoms, most crystals do not consist of repeated unit cells." is false.

Which of the following statements about crystals is false?Single choice

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