Solid State MCQ Questions & Answers in Physical Chemistry | Chemistry

Non-stoichiometric compounds are chemical compounds with an elemental composition that cannot be represented by a ratio of well-defined natural numbers, and are therefore in violation of the law of definite proportions. They are most often solids that contain random defects, resulting in the deficiency of one element. So, none of given option is correct.

Number of tetrahedral voids per atom in a unit cell is 2. Hence, the total number of tetrahedral voids $$= 2n.$$

In a $$fcc$$  lattice, the distance between the cation and anion is equal to the sum of their radii, which is equal to half of the edge length of unit cell,
$$\eqalign{ & {\text{i}}{\text{.e}}{\text{.}}\,\,{r^ + } + {r^ - } = \frac{a}{2}\,\,{\text{(where }}a = {\text{edge length)}} \cr & {{\text{r}}^ + } = 95\,pm,\,{r^ - } = 181\,pm \cr & {\text{Edge length}} \cr & = 2{r^ + } + 2{r^ - } = \left( {2 \times 95 + 2 \times 181} \right)pm \cr & = \left( {190 + 362} \right)pm \cr & = 552\,pm. \cr} $$

When equal number of cations and anions are missing from their regular lattice positions, we have schottky defect. This type of defects are more common in ionic compounds with high co-ordination number and where the size of positive and negative ions are almost equal e.g. $$NaCl$$  $$KCl$$  ete.

$$n$$ - type, since electron is set free.

Increase of pressure increases coordination number. Hence, by applying high pressure, $$NaCl$$  type crystal can be changed into $$CsCl$$  type crystal.

$$KBr$$  ionic solid shows Schottky defect.

Packing fraction is defined as the ratio of the volume of the unit cell that is occupied by the spheres to the volume of the unit cell.
$$P-F.$$  for $$cpp$$  and $$bcc$$  are 0.74 and 0.68 respectively.
So, the free space in $$ccp$$  and $$bcc$$  are 26% & 32% respectively.

Doping of germanium with arsenic ( or other group-15 element ) gives rise to $$n$$ - type semiconductor.

$${I_{2\left( s \right)}}$$  is a non-polar molecular solid and is an insulator. $${H_2}{O_{\left( s \right)}}$$  is a hydrogen bonded molecular solid and is an insulator. $$Mg$$  is metallic solid and is a conductor in solid as well as in molten state. $$TiO$$  is an ionic solid and is an insulator in solid state but is a conductor in molten state and in aqueous solutions.