Calculate the number of atoms present in $1.58 \ g$ of a metal that forms a $bcc$ structure,given that $\varrho \times a^3 = 1.58 \times 10^{-22} \ g$.

Give the correct order of initials $T$ (true) or $F$ (false) for the following statements:
$I.$ In an anti-fluorite structure,anions form $FCC$ lattice and cations occupy all tetrahedral voids.
$II.$ If the radius of cations and anions are $0.2 \ \mathring{A}$ and $0.95 \ \mathring{A}$,then the coordination number of the cation in the crystal is $4$.
$III.$ An atom/ion is transferred from a lattice site to an interstitial position in a Frenkel defect.
$IV.$ The density of a crystal always increases due to a substitutional impurity defect.

Which of the following statements is correct?

Match the following:

List-$I$	List-$II$
$A$. $ABCABC...$ layers	$I$. $F$-centres
$B$. Thermodynamics defects	$II$. $X$-ray diffraction
$C$. $Farbenzenter$	$III$. Vacancy defects
$D$. $Debye-Scherrer$ method	$IV$. Semiconductors
	$V$. Silver

$A$ body-centred cubic $(BCC)$ element of density $10.3 \ g \ cm^{-3}$ has a cell edge of $314 \ pm$. Calculate the atomic mass of the element. Also, Lithium borohydride crystallizes in an orthorhombic system with four molecules per unit cell. The unit cell dimensions are $a = 6.8 \ \mathring{A}$, $b = 4.4 \ \mathring{A}$, and $c = 7.2 \ \mathring{A}$. If the molar mass is $21.76 \ g \ mol^{-1}$, calculate the density of the crystal.

$A$ mixture of $KCl$ and $KF$ is added to sodium chloride.