In FCC unit cell, what fraction of edge is not covered by atoms? — Solid State Chemistry Question

💡 Solution & Explanation

In an FCC cell, the edge length is $a$. The atoms at the corners cover a distance of $2r$ along the edge. We know $4r = \sqrt{2}a$, so $2r = \frac{\sqrt{2}}{2}a \approx 0.707a$. The fraction covered is $0.707$. The fraction not covered is $1 - 0.707 = 0.293$. Therefore, correct answer is B.