Select the correct statement.

$A$ 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.

Atoms of metals $x$,$y$,and $z$ form face-centred cubic $(fcc)$ unit cell of edge length $L_x$,body-centred cubic $(bcc)$ unit cell of edge length $L_y$,and simple cubic unit cell of edge length $L_z$,respectively. If $r_z = \frac{\sqrt{3}}{2} r_y$; $r_y = \frac{8}{\sqrt{3}} r_x$; $M_z = \frac{3}{2} M_y$ and $M_z = 3 M_x$,then the correct statement$(s)$ is (are) [Given: $M_x$,$M_y$,and $M_z$ are molar masses of metals $x$,$y$,and $z$,respectively. $r_x$,$r_y$,and $r_z$ are atomic radii of metals $x$,$y$,and $z$,respectively.]
$(A)$ Packing efficiency of unit cell of $x >$ Packing efficiency of unit cell of $y >$ Packing efficiency of unit cell of $z$
$(B)$ $L_y > L_z$
$(C)$ $L_x > L_y$
$(D)$ Density of $x >$ Density of $y$

An element crystallizes in a body-centred cubic $(BCC)$ structure with an edge length of $400 \ pm$. Calculate the interatomic distance in the crystal. Additionally, if an atom has a radius of $300 \ pm$ and crystallizes in a face-centred cubic $(FCC)$ lattice, calculate the distance between the nearest neighbours.

Silver (atomic weight $= 108 \ g \ mol^{-1}$) has a density of $10.5 \ g \ cm^{-3}$. The number of silver atoms on a surface of area $10^{-12} \ m^2$ can be expressed in scientific notation as $y \times 10^x$. The value of $x$ is

Which one of the following statements is not correct?