Hexagonal close packing $(HCP)$ is found in the crystal lattice of:

An ionic compound is formed between a metal $M$ and a non-metal $Y$. If $M$ occupies half the octahedral voids in the cubic close-packed arrangement formed by $Y$,the chemical formula of the ionic compound is

In the face-centered unit cell,the lattice points are present at

Element '$B$' forms $ccp$ structure and '$A$' occupies half of the octahedral voids,while oxygen atoms occupy all the tetrahedral voids. The structure of bimetallic oxide is

Calculate the packing efficiency in a simple cubic metal crystal.

In chrysoberyl,a compound containing beryllium,aluminium and oxygen,oxide ions form a cubic close-packed structure. Aluminium ions occupy $\frac{1}{4}$ of the octahedral voids and beryllium ions occupy $\frac{1}{8}$ of the tetrahedral voids. The formula of the compound is