The most unsymmetrical crystal system is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Triclinic
The seven crystal systems differ in the relations between the edge lengths a, b, c and the angles α, β, γ of the unit cell. The fewer the equalities, the lower the symmetry. In the triclinic system all three edges are unequal and all three angles are unequal, none being 90°:
\( \displaystyle a \ne b \ne c,\qquad \alpha \ne \beta \ne \gamma \ne 90^\circ \)
Examples are \( \ce{K2Cr2O7} \), \( \ce{CuSO4.5H2O} \) and \( \ce{H3BO3} \). So triclinic is the most unsymmetrical crystal system.
Option (1) Tetragonal — Incorrect. a = b ≠ c and all three angles 90°, a fairly symmetrical cell.
Option (2) Hexagonal — Incorrect. a = b ≠ c, with α = β = 90° and γ = 120°.
Option (4) Rhombohedral — Incorrect. a = b = c and α = β = γ ≠ 90°; all edges and all angles are equal.
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.