21753.For a crystal, the angle of diffraction (2θ) is 90° and the second order line has a d value of 2.28Å. The wavelength (in Å) of X–rays usedfor Bragg's diffraction is
2.28
2.00
1.613
4.00
21754.Lithium has a bcc structure. Its density is 530 kg m–3 and its atomic mass is 6.94 g mol–1. Calculate the edge length of a unit cell of Lithium metal (NA = 6.02 × 1023 mol–1)
527 pm
264 pm
154 pm
352 pm
21755.If AgI crystallizes in zinc blende structure with I– ions at lattice points, what fraction of tetrahedral voids is occupied by Ag+ ions?
25%
50%
100%
75%
21756.If the distance between Na+ and Cl– ions in sodium chloride crystal is X pm, the length of the edge of the unit cell is
4 X pm
2 X pm
X/2 pm
X/4 pm
21757.If Z is the number of atoms in the unit cell that represents the closest packing sequence ABC ABC_____, the number of tetrahedral voids in the unit cell is equal to
Z
2Z
Z/2
Z/4
21759.In a face centred cubic lattice, atom A occupies the corner positions and atom B occupies the face centre positions. If one atom of B is missing from one of the face centred points, the formula of the compound is
A2B5
A2B
AB2
A2B3
21760.Total number of tetrahedral and octahedral voids in 0.5 mol of a compound forming hcp structure are:
6.022 × 1023
3.011 × 1023
9.033 × 1023
4.516 × 1023
21761.In AgBr, there can occur
only Schottky defect
only Frenkel defect
Both (a) and (b)
Neither (a) nor (b)
21762.If NaCl is doped with 10–4 mol % of SrCl2, the concentration of cation vacancies will be (NA= 6.02 × 1023 mol–1)
6.02 × 1016 mol–1
6.02 × 1017 mol–1
6.02 × 1014 mol–1
6.02 × 1015 mol–1
21763.In an antifluorite structure, cations occupy
tetrahedral voids
centre of cube
octahedral voids
corners of cube
21764.In Na2O having antifluorite structure
Oxide ions have a cubic close packed arrangement and Na+ occupy all the eight tetrahedral voids.
Oxide ions have a cubic close packed arrangement and Na+ occupy all the octahedral voids
Na+ ions have a cubic close arrangement and O2- occupy all the octahedral voids
Na+ ions have a cubic close arrangement and O2– occupy all the tetrahedral voids.
21765.Which one of the following defects in the crystals lowers its density?
F–centres
Schottky defect
Frenkel defect
Interstitial defect
21766.Relationship between atomic radius (r) and the edge length (a) of a body centred cubic unit cell is
r = $\dfrac{a}{2}$
r = $\sqrt{\dfrac{a}{2}}$
r = $\dfrac{\sqrt{3}{4}}a$
r = $\dfrac{3a}{2}$
21767.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 m2 can be expressed in scientific notation as y × 10$x$. The value of $x$ is
13
9
7
5
21768.Which is not the correct statement for ionic solids in which positive and negative ions are held by strong electrostatic attractive forces?
The radius ratio increases as coordination number increases
As the difference in size of ions increases coordination number increases
When coordination number is eight, the radius ratio lies between 0.225 to 0.414
In ionic solid of the type AX (ZnS, Wurtzite) the coordination number of Zn2+ and S2– respectively are 4 and 4
21769.An ionic compound is expected to have tetrahedral structure if r+/r– lies in the range of
0.414 to 0.732
0.732 to 1
0.155 to 0.225
0.225 to 0.414
21771.A unit cell of sodium chloride has four formula units. The edge length of the unit cell is 0.564 nm. What is the density of sodium chloride?
1.2 g/cm3
2.16 g/cm3
3.64 g/cm3
4.56 g/cm3
21772.The ability of a given substance to assume two or more crystalline structure is called
polymorphism
isomorphism
amorphous
isomerism