b) Atoms of element B form hep lattice and those of element A occupies `2//3^(rd)` of tetrahedral voids. Calculate the formula of the compound formed by A and B. 

Explanation

The hcp lattice is formed by the atoms of the element B.
Here, the number of tetrahedral voids generated is equal to twice the number of atoms of the element B.
The atoms of element A occupy `(2)/(3)` rd of the tetrahedral voids.
Therefore, the number of atoms of A is equal to `2 xx (2)/(3) = (4)/(3)` rd of the number of atoms of B.
Therefore, ratio of the number of atoms of A to that of B is
`A : B = (4)/(3) : 1`
= 4 : 3
Thus the formula of the compound ia `A_(4) B_(3)`.