Percentage of free space in a body centred cubic unit cell is 

• 30%

• 32%

• 34%

• 34%

With which one of the following elements silicon should be doped so as to give p - type of semiconductor?

• Germanium

• Arsenic

• Selenium 

• Selenium 

The fraction of totoal volume occupied by the atoms present in a simple cube is: 

• π/6

• 
• 
• 

If NaCl is doped with 10^-4 mol% of SrCl₂ the concentration of cation vacancies will be 
(N_A = 6.02 x 10²³ mol^-1):

• 6.02 x 10¹⁵ mol^-1

• 6.02 x 10¹⁶ mol^-1

• 6.02 x 10¹⁷

• 6.02 x 10¹⁷

CsBr crystallises in a body centred cubic lattice. The unit cell length is 436.6 pm. Given that the atomic mass of Cs - 133 and that of Br = 80 amu and Avogadro number being
6.02 x 10²³ mol^-1, the density of CsBr is:

• 42.5 g/cm³

• 0.425 g/cm³

• 8.25 g/cm³

• 8.25 g/cm³

The appearance of colour is solid alkali metal halides is generally due to:

• F- centres

• Schottky defect

• Frenkel defect

• Frenkel defect

Which is the incorrect statement?

• FeO_0.98 has non stoichiometric metal deficiency defect

• Density decreases in case of crystals with Schottky's defect

• NaCl(s) is insulator, silicon is semiconductor,silver is conductor, quartz is piezo electric crystal

• NaCl(s) is insulator, silicon is semiconductor,silver is conductor, quartz is piezo electric crystal

168.

Iron exhibits bcc structure at room temperature. Above 900°C, it transforms to fcc structure. The ratio of density of iron at room temperature to that at 900°C (assuming molar mass and atomic radii of iron remains constant with temperature) is

• $\frac{\sqrt{3}}{\sqrt{2}}$

• $\frac{4\sqrt{3}}{3\sqrt{2}}$

• 1/2

• $\frac{3\sqrt{3}}{4\sqrt{2}}$

A solid AB has a NaCl structure. If the radius of cation A⁺ is 170 pm, then the maximum possible radius of the anion B^- is

• 397.4 pm

• 347.9 pm

• 210.9 pm

• 410.6 pm

If oxide ions are arranged in hep and the aluminium ions occupy two thirds of octahedral voids. What will be the formula of the compound?

• AlO₃ 

• Al₂O₃

• (Al₂O₃)₂

• Al₃O₄