Match List - I with List - II.
|
List – I |
List – II |
|
(A) Cubic |
(I) a = b ≠ c; α = β = 90°, γ = 120° |
|
(B) Tetragonal |
(II) a ≠ b ≠ c; α = β = γ = 90° |
|
(C) Orthorhombic |
(III) a = b ≠ c; α = β = γ = 90° |
|
(D) Hexagonal |
(IV) a = b = c; α = β = γ = 90° |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
Each crystal system is defined by its unit-cell parameters: the three edge lengths a, b, c and the three angles α, β, γ. Tetragonal and hexagonal cells both have a = b ≠ c; they are told apart by the angles (all 90° in tetragonal, γ = 120° in hexagonal).
(A) Cubic — This matches (IV) a = b = c; α = β = γ = 90°. All three edges are equal and all angles are right angles (NaCl, Cu).
(B) Tetragonal — This matches (III) a = b ≠ c; α = β = γ = 90°. Two edges are equal, the third is different, and all angles are 90° (white tin, \( \ce{TiO2} \)).
(C) Orthorhombic — This matches (II) a ≠ b ≠ c; α = β = γ = 90°. All three edges are different, but all angles are still 90° (rhombic sulphur, \( \ce{KNO3} \)).
(D) Hexagonal — This matches (I) a = b ≠ c; α = β = 90°, γ = 120°. Two edges are equal and the angle between them is 120° (graphite, ZnO).
Shortcut: (C)-(II) (orthorhombic, all edges different) appears only in Option (2).
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):
Primitive and Centred Unit Cells – …
