Interionic distance for CsCl crystal is

• a

• $\frac{\mathrm{a}}{2}$

• $\frac{\sqrt{3}}{4}\mathrm{a}$

• $\frac{2\mathrm{a}}{\sqrt{3}}$

72.

How many space lattices are obtained from the different crystal systems?

• 7

• 14

• 32

• 230

Which of the following statements about ionic crystals is false?

• Melting and boiling temperature of ionic crystals are very high

• These are soluble in water and other solvent

• At low temperature in sold state they are good conductor of electricity.

• They have high cohesive energy

The structure of ionic compound with Schottky defects has

• same number of cationic and anionic vacancies

• anionic vacancy and interstitial anion

• cationic vacancies

• cationic vacancies and interstitial cation

If a pentavalent impurity is mixed in the crystal-lattice of germanium then the semiconductor formed will be

• p-type semiconductor

• n-type semiconductor

• (a) and (b) both

• None of the above

A compound formed by elements X and Y crystallises in a cubic structure in which the X atoms are at the comers of a cube and the Y atoms are at the face centres. The formula of the compound is

• XY₃

• X₃Y

• XY

• XY₂

In a face centred cubic lattice, a unit cell is shared equally by how many unit cells?

• 4

• 2

• 6

• 8

The number of Na⁺ ions filling all octahedral voids in NaCl structure is

• 6

• 12

• 13

• 14

A solid metal has ccp or fcc structure. The relation of side of cube (a) and radius of atom (r) will be

• a= 2r

• a= 2√2r

• $\mathrm{a}= \frac{4}{\sqrt{3\mathrm{r}}}$

• $\mathrm{a}= \sqrt{\frac{3}{2}}\mathrm{r}$

The flame colours of metal ions are due to

• Schottky defect

• Frenkel defect

• metal excess defect

• metal deficiency defect