Exercise 1

In the solid state, $\mathrm{MgO}$ has the same structure as that of sodium chloride. The number of oxygens surrounding each magnesium in $\mathrm{MgO}$ is:

A compound is formed by elements $\mathrm{A}$ and $\mathrm{B}$. The crystalline cubic structure has $\mathrm{A}$ atoms at the corners of the cube and $\mathrm{B}$ atoms at the body centre. The simplest formula of the compound is:

When molten zinc is converted into solid state, it acquires HCP structure. The number of nearest neighbours will be:

The pyknometric density of sodium chloride crystal is $2.165$$\times {10}^3 \mathrm{kg} {\mathrm{m}}^{-3}$ , while its $\mathrm{X}$-ray density is $2.178\times {10}^3 \mathrm{kg} {\mathrm{m}}^{-3}$. The fraction of unoccupied sites in sodium chloride crystal is:

A compound formed by elements $\mathrm{X}$ and $\mathrm{Y}$ crystallizes in a cubic structure in which the $\mathrm{X}$ atoms are at the corners of a cube and the $\mathrm{Y}$ atoms are at the face centres. The formula of the compound is:

The density of solid argon is $1.65 \mathrm{g}$ per $\mathrm{cc}$ at $-233 °\mathrm{C}$. If the argon atom is assumed to be a sphere of radius $1.54\times {10}^{-8}$ $\mathrm{cm},$ what per cent of solid argon is apparently empty space? $(\mathrm{Ar}=40)$

The appearance of colour in solid alkali metal halides is generally due to

$\mathrm{CsBr}$ crystallises in a body centred cubic lattice. The unit cell length is $436.6 \mathrm{pm}$. Given that, the atomic mass of $\mathrm{Cs}=133$ and that of $\mathrm{Br}=80$ $\mathrm{amu}$ and Avogadro number being $6.02\times {10}^{23} {\mathrm{mol}}^{-1}$, the density of $\mathrm{CsBr}$ is: