The edge lengths of the unit cells in terms of the radius of spheres constituting fcc, bcc & simple cubic 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 cubic: 2√2 r, 4r/√3, 2r.
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.