The maximum radius of a sphere that can be fitted in the octahedral hole of a cubical closed packing of spheres of radius $r$ is $..............$ $r$.

How will you distinguish between the following pairs of terms:
$(i)$ Hexagonal close-packing $(hcp)$ and cubic close-packing $(ccp)$?

The number of tetrahedral voids per unit $HCP$ cell is

In a $ccp$ structure of $X$ atoms,$Y$ atoms occupy half of the octahedral voids. If one $X$ atom and one $Y$ atom in each unit cell are replaced by a $Z$ atom,the molecular formula of the solid will be:

$A$ compound is formed by two elements $A$ and $B$. The element $B$ forms a cubic close-packed $(CCP)$ structure and atoms of $A$ occupy $\frac{1}{3}$ of the tetrahedral voids. If the formula of the compound is $A_x B_y$,then the value of $x+y$ is:

The molecular formula of a crystalline solid is $X_3Y_2$. Atoms of $Y$ form $ccp$ lattice,and atoms of $X$ occupy $50\%$ octahedral voids and $x\%$ of tetrahedral voids. What is the percentage of unoccupied tetrahedral voids?