Problem 110
A metallic element crystallizes into a lattice containing a sequence of layers of \(\mathrm{ABABAB} \ldots\) Any packing of spheres leaves out voids in the lattice. What percentage by volume of this lattice is empty space? (a) \(26 \%\) (b) \(74 \%\) (c) \(50 \%\) (d) \(85 \%\)
Problem 111
Gold (Au) crystallizes in cubic close packed (FCC). The atomic radius of gold is \(144 \mathrm{pm}\) and the atomic mass of \(\mathrm{Au}=197.0 \mathrm{amu}\). The density of \(\mathrm{Au}\) is (a) \(19.4 \mathrm{~g} \mathrm{~cm}^{-3}\) (b) \(194 \mathrm{~g} \mathrm{~cm}^{-3}\) (c) \(39.4 \mathrm{~g} \mathrm{~cm}^{-3}\) (d) \(0.194 \mathrm{~g} \mathrm{~cm}^{-3}\)
Problem 112
An alloy of copper, silver and gold is found to have copper constituting the cop lattice. If silver atoms occupy the edge centres and gold is present at body centre, the alloy will have the formula (a) \(\mathrm{Cu}_{4} \mathrm{Ag}_{4} \mathrm{Au}\) (b) \(\mathrm{Cu} \mathrm{Ag} \mathrm{Au}\) (c) \(\mathrm{Cu}_{4} \mathrm{Ag}_{2} \mathrm{Au}\) (d) \(\mathrm{Cu}_{4} \mathrm{Ag}_{3} \mathrm{Au}\)
Problem 113
At room temperature, sodium crystallizes in a BCC lattice with the cell edge (a) \(4.24 \AA\). Find the density of sodium. (Atomic wt of \(\mathrm{Na}=23\) ) (a) \(2.01 \mathrm{~g} / \mathrm{cm}^{3}\) (b) \(1.002 \mathrm{~g} / \mathrm{cm}^{3}\) (c) \(3.003 \mathrm{~g} / \mathrm{cm}^{3}\) (d) \(2.004 \mathrm{~g} / \mathrm{cm}^{3}\)
Problem 114
The density of solid argon is \(1.65 \mathrm{~g} / \mathrm{mL}\) at \(-233^{\circ} \mathrm{C}\). If the argon atom is assumed to be sphere of radius \(1.54 \times\) \(10^{-8} \mathrm{~cm}\), what percentage of solid argon is apprarently empty space? (Atomic wt of \(\mathrm{Ar}=40\) ) (a) \(32 \%\) (b) \(52 \%\) (c) \(62 \%\) (d) \(72 \%\)
Problem 116
Identify the correct statements. (a) The size of octahedral site is given by \(\mathrm{r}=0.414 \mathrm{R}\) where \(\mathrm{r}\) is the radius of octahedral hole and \(\mathrm{R}\) is the radius of spheres enclosing it. (b) In CCP or HCP arrangement, there are two octahedral sites per closely packed sphere. (c) The centres of octahedral sites lie at the mid point of the sides and at the body centre of face centred cubic unit cell. (d) The radius of tetrahedral hole (r) and that of spheres (R) forming it are related as \(\mathrm{r}=0.155 \mathrm{R}\).
Problem 117
The correct statements regarding defects in solids are, (a) Schottky defects affect the density of solid. (b) Trapping of an electron in the lattice leads to the formation of \(\mathrm{F}\) - center. (c) Frenkel defect is a dislocation effect. (d) Frenkel defect is usually favoured by a very small difference in the sizes of cation and anion.
Problem 118
What will be the distance between two nearest neighbour in primitive, fcc and bec unit cell? (a) For bec, \(\mathrm{d}=1.414 \mathrm{a}\) (b) For bec, \(\mathrm{d}=1.726 \mathrm{a}\) (c) For primitive, \(\mathrm{d}=\mathrm{a}\) (d) For fcc, \(\mathrm{d}=0.707 \mathrm{a}\)
Problem 119
\(\mathrm{Fe}_{3} \mathrm{O}_{4}\) has spinal structure. Which is not true about this solid? (a) Number of \(\mathrm{O}^{2-}>\mathrm{Fe}^{3+}>\mathrm{Fe}^{2+}\) (b) Coordination number of \(\mathrm{Fe}^{3+}=8\) through out the unit cell. (c) \(\mathrm{Fe}^{3+}\) ions are equally distributed between octahedral and tetrahedral voids. (d) Tetrahedral voids are equally distributed between \(\mathrm{Fe}^{2+}\) and \(\mathrm{Fe}^{3+}\) ions.
Problem 125
$$ \begin{aligned} &\text { Match the following: }\\\ &\begin{array}{ll} \hline \begin{array}{l} \text { Column-I } \\ \text { (Unit cell type) } \end{array} & \begin{array}{l} \text { Column-II } \\ \text { (Unit cell shapes) } \end{array} \\ \hline \begin{array}{ll} \text { (a) Simple or Primitive } & \text { (p) Cubic } \\ \text { (b) Body centered } & \text { (q) Orthorhombic } \\ \text { (c) Face centred } & \text { (r) Tetragonal } \\ \text { (d) End centred } & \text { (s) Monoclinic } \\ \text { (t) Triclinic } \end{array} \\ \hline \end{array} \end{aligned} $$
