Solid State MCQ Questions & Answers in Physical Chemistry | Chemistry
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51.
An element crystallising in body centred cubic lattice has an edge length of 500 $$pm.$$ If its density is $$4\,g\,c{m^{ - 3}},$$ the atomic mass of the element $$\left( {{\text{in}}\,\,g\,\,mo{l^{ - 1}}} \right)$$ is $$\left( {{\text{consider}}\,\,{{\text{N}}_A} = 6 \times {{10}^{23}}} \right)$$
52.
A solid is made of two elements $$X$$ and $$Z.$$ The atoms $$Z$$ are in $$ccp$$ arrangement while the atoms $$X$$ occupy all the tetrahedral sites. What is the formula of the compound?
A
$$XZ$$
B
$$X{Z_2}$$
C
$${X_2}Z$$
D
$${X_2}{Z_3}$$
Answer :
$${X_2}Z$$
Let the number of $$Z$$ atoms in the $$ccp$$ arrangement = 100
Thus the number of tetrahedral sites = 200
Since all the tetrahedral sites are occupied by $$X$$ atoms, the number of $$X$$ atoms = 200
Hence ratio of $$X : Z = 2 : 1$$
Thus the formula is $${X_2}Z$$
53.
In a solid $$'AB'$$ having the $$NaCl$$ structure, $$'A'$$ atoms occupy the corners of the cubic unit cell. If all the face-centered atoms along one of the axes are removed, then the resultant stoichiometry of the solid is
A
$$A{B_2}$$
B
$${A_2}B$$
C
$${A_4}{B_3}$$
D
$${A_3}{B_4}$$
Answer :
$${A_3}{B_4}$$
$$\eqalign{
& {\text{Effective number of}}\,\,\,'A'\,\,{\text{atoms}} \cr
& = \left( {8 \times \frac{1}{8}} \right) + \left( {4 \times \frac{1}{2}} \right) = 3 \cr
& {\text{Effective number of}}\,\,\,'B'\,\,{\text{atoms}} \cr
& = \left( {12 \times \frac{1}{4}} \right) + 1 = 4 \cr
& \therefore \,{\text{ Formula of the solid}} = {A_3}{B_4}. \cr} $$
54.
Which of the following statements is not correct about molecular crystals ?
A
They are generally soft and easily compressible.
B
They are good conductors of electricity as the electrons are delocalised in the bonds.
C
They have low melting and boiling points.
D
They consist of polar or non-polar molecules.
Answer :
They are good conductors of electricity as the electrons are delocalised in the bonds.
Molecular crystals are bad conductors of electricity as the electrons are localised in the bonds.
55.
Which of the following is not a characteristic of a crystalline solid ?
A
Definite and characteristic heat of fusion
B
Isotropic nature
C
A regular periodically repeated pattern of arrangement of constituent particles in the entire crystal
D
A true solid
Answer :
Isotropic nature
Crystalline solids are anisotropic in nature.
56.
Edge length of a cube is 400$$\,pm.$$ Its body diagonal would be
A
500$$\,pm$$
B
566$$\,pm$$
C
600$$\,pm$$
D
693$$\,pm$$
Answer :
693$$\,pm$$
Body diagonal $$(d)$$ of a cubic crystal of edge length $$(a)$$ is given by,
$$\eqalign{
& d = a\sqrt 3 \cr
& {\text{putting}}\,\,a = 400\,pm,{\text{we get}} \cr
& d = \sqrt 3 \times 400\,pm = 692.8\,pm \approx 693\,pm. \cr} $$
57.
The number of atoms in $$100\,g$$ of an $$fcc$$ crystal with density, $$d = 10\,g/c{m^3}$$ and cell edge equal to $$100\,pm,$$ is equal to
58.
A $$NaCl$$ crystal is changed into $$CsCl$$ type structure by :
A
Increasing temperature and decreasing pressure.
B
Increasing pressure and decreasing temperature.
C
Increasing both temperature and pressure
D
None of these.
Answer :
Increasing pressure and decreasing temperature.
Low co-ordination compound can be changed into high co-ordination compound
by increasing pressure and decreasing temperature.
59.
An ionic compound has a unit cell consisting of $$A$$ ions at the corners of a cube and $$B$$ ions on the centres of the faces of the cube. The empirical formula for this compound would be
A
$${A_3}B$$
B
$$A{B_3}$$
C
$${A_2}B$$
D
$$AB$$
Answer :
$$A{B_3}$$
Number of A ions in the unit cell $$ = \frac{1}{8} \times 8 = 1$$
Number of B ions in the unit cell $$ = \frac{1}{2} \times 6 = 3$$
Hence empirical formula of the compound = $$A{B_3}$$
60.
An element ( atomic mass $$= 100 g / mol$$ ) having $$bcc$$ structure has unit cell edge $$400\,pm.$$ Then, density of the element is