Close Packed Structures — Prelims Questions

Which of the following statements about close-packed structures is INCORRECT?

A compound is formed by elements X and Y. Atoms of element Y (anions) form a cubic close-packed (CCP) lattice, and atoms of element X (cations) occupy 2/3rd of the tetrahedral voids. What is the formula of the compound?

Which of the following metals crystallizes in a hexagonal close-packed (HCP) structure?

What is the coordination number of an atom in a 2D hexagonal close-packed layer?

If the radius of an atom in a close-packed structure is 'r', what is the radius of the largest sphere that can fit into an octahedral void?

Which of the following stacking sequences represents a cubic close-packed (CCP) structure?