The regular three dimensional arrangement of points in a crystal is known as crystal lattice and the smallest repeating pattern in the lattice is called unit cell. The unit cells are characterised by the edge lengths a, b, c and the angles between them `alpha, beta and gamma` respectively. Based on this, there are seven crystal systems. In a cubic unit cell:
`a=b=c and alpha = beta=gamma=90^(@)` The number of points in simple, body centred and face centred cubic cells are 1,2 and 4 respectively In both the hcp and ccp of spheres, the number of tetrahedral voids per sphere is two while the octahedral voids is one.
A double triangular void surrounded by three spheres above and three spheres below is called

Options

A. triangular void
B. tetrahedral void
C. octahedral void
D. trigonal bipyramidal void.

Answer

C

Explanation

A double triangular void surrounded by 6 spheres is octahedral void.