Atoms of element B form hcp lattice and those of the element A occupy `2//3^("rd")` of tetrahedral voids . What is the formula of the compound formed by the element A and B ?

Explanation

Atoms B adopt hcp arrangement and there are two tetrahedral sites per atom of B. Since `2//3` rd of the tetrahedral sites are occupied by atoms of element A, then for each of B, the number of A atoms will be `2 xx 2//3 = 4//3`.
Ratio of atoms A and B = `4/3 : 1 = 4 : 1`
`:.` Formula of compound : `A_4B_3`.