An element crystallises in fcc lattice having edge length 350 pm. Maximum radius of the atom which can be placed in the interstitial site without distorting the structure is

For fcc structure, (r+r-)=0.414 for octahedral void             = 0.225 for tetrahedral void Thus, maximum packing can be octahedral void∴r+=0.414r-Also, r-=a22∴r+=0.414a22=0.414×35022=144.922=51.23pm