Solid NaCl is:
A. amorphous
B. crystalline
C. anisotropic
D. isotropic
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → B & C only
Sodium chloride is an ionic solid in which \( \ce{Na^{+}} \) and \( \ce{Cl^{-}} \) ions are arranged in a regular, repeating three-dimensional pattern (long range order). Such solids are crystalline, and because the arrangement of particles is different along different directions, their physical properties (refractive index, electrical resistance) differ with direction: they are anisotropic.
A. amorphous — Incorrect. Amorphous solids (glass, rubber) have only short range order; NaCl has a regular lattice.
B. crystalline — Correct. NaCl has a definite cubic lattice and a sharp melting point.
C. anisotropic — Correct. Its properties depend on the direction of measurement, as for all crystalline solids.
D. isotropic — Incorrect. Isotropy (same value in all directions) is a property of amorphous solids.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Amorphous and Crystalline Solids – “… Crystalline solids are anisotropic in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystals. This arises from different arrangement of particles in different directions.”