A metal crystallizes in a closed packed structure, the atoms stack together occupying maximum space & leaving minimum vacant space. Each sphere in the first layer is in contact with six neighbours. Now while arranging the second layer on the first layer, spheres are placed in depression of first layer. S pheres of third layer lie in the depression of second layer, that do not lie directly over the atoms of first layer. This repeating arrangement of atoms produces a giant lattice.

(i) If edge length of unit cell is ‘a’ what is the shortest distance between two atoms –