In a pure crystal, the lattice point cannot be occupied by _______.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → an electron
A crystal lattice is a regular three-dimensional arrangement of points in space. Each point, called a lattice point, represents one constituent particle of the solid, and the particle may be an atom, a molecule or an ion (or a group of them). Joining the lattice points by straight lines gives the geometry of the lattice.
An electron is not a constituent particle of this kind. Electrons belong to the atoms or ions that sit at the lattice points; in a pure, perfect crystal no lattice point is occupied by an electron alone. (Electrons trapped in anion vacancies, the F-centres, appear only in a defective crystal, such as NaCl heated in sodium vapour.) So the lattice point cannot be occupied by an electron.
Option (1) an atom — Can occupy a lattice point. For example, Cu atoms in copper metal or C atoms in diamond.
Option (2) a molecule — Can occupy a lattice point. For example, \( \ce{I2} \) molecules in solid iodine or \( \ce{H2O} \) molecules in ice.
Option (3) an ion — Can occupy a lattice point. For example, \( \ce{Na^+} \) and \( \ce{Cl^-} \) ions in sodium chloride.
Option (4) an electron — Cannot occupy a lattice point. An electron is not a constituent particle of the solid; it belongs to the atoms or ions at the lattice points.
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):
Crystal Lattices and Unit Cells – …
