The edge lengths of the unit cells in terms of the radius of spheres constituting fcc, bcc, and simple unit cell respectively are:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(2\sqrt{2}r, \frac{4r}{\sqrt{3}}, 2r\)
fcc (ccp): spheres touch along the face diagonal, so face diagonal b = 4r = √2 a, giving a = 2√2 r.
bcc: spheres touch along the body diagonal, so body diagonal c = 4r = √3 a, giving a = 4r/√3.
Simple cubic: spheres touch along the edge, so a = 2r.
In the order fcc, bcc, simple: 2√2 r, 4r/√3, 2r.
Note 1: 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.
Note 2: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | – | 02-06 S3 31-05 S1 | – |