(i)Tetrahedral voids: Surrounded by 4 speres which lie at the verticles of regular tetrahedron
Octahedral void: surrounded by 6 speres and formmed by combination of 2 triangular voids of 1st and 2nt lager
(ii) Crystal lattice : 3-Darrangement of particles in space
unit cell : smallest unit of crystal lattice when repeated in different direction generates the entire lattice