In a pure Face-Centred Cubic (FCC) lattice, what exact fraction of the unit cell edge length is NOT — Solid State Chemistry Question

💡 Solution & Explanation

In FCC, atoms touch along the face diagonal, so $4r=\sqrt{2}a$ and $2r/a=1/\sqrt{2}=0.707$. Along a unit-cell edge, the uncovered fraction is $1-0.707=0.293$.