Efficiency of packing in body centered cubic structures is found to be:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 68%
The atoms touch along the body diagonal, so √3a = 4r; a bcc cell holds 2 atoms, and
\( \displaystyle \text{Packing efficiency} = \frac{2 \times \frac{4}{3}\pi r^3}{\left(\frac{4r}{\sqrt{3}}\right)^3} \times 100 = 68\% \)
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):
Efficiency of Packing in Body-Centred Cubic Structures – …
