What is the coordination number of a one-dimensional close-packed arrangement?

$A$ two-dimensional solid is made by alternating circles with radius $a$ and $b$ such that the sides of the circles touch. The packing fraction is defined as the ratio of the area under the circles to the area under the rectangle with sides of length $x$ and $y$. The ratio $r=b/a$ for which the packing fraction is minimised is closest to $.....$

What is the total number of spheres that surround the tetrahedral hole in a close-packed three-dimensional structure?

For the given close-packed structure of a salt made of cation $X$ and anion $Y$ shown below (ions of only one face are shown for clarity),the packing fraction is approximately
$\text{(packing fraction} = \frac{\text{Packing efficiency}}{100}\text{)}$

In a close-packed lattice,how does the size of an octahedral void compare to that of a tetrahedral void?

The stacking pattern in a body-centered cubic $(bcc)$ lattice is of the type............