This set of Solid State Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Definitions”.
1. The smallest repetitive unit of the crystal structure is known as____________
c) Unit cell
Explanation: Crystal is built up of a regular arrangement of atoms in three dimensions, this arrangement can be represented by a repeat unit or motif called unit cell, thus unit cell is defined as the smallest repeating unit which shows the full symmetry of the crystal structure.
2. Crystals in which the number of the combinations of the symmetric molecule is limited to 32 is known as _________
a) Crystallographic unit cell
b) Crystallographic point groups
c) Crystallographic crystals
d) Crystallographic atoms
Explanation: Many molecules and crystals possess more than one element of point symmetry, but the number of combinations of the symmetric molecule is limited to 32, these are known as crystallographic point groups.
3. Which of the following unit cell has all the angles at 90˚ but the sides are of unequal length?
a) Monoclinic unit cell
b) Orthorhombic unit cell
c) Triclinic unit cell
d) Hex clinic unit cell
Explanation: The orthorhombic unit cell may be regarded as something like a shoebox in which the angles are all 90˚ but the sides are of unequal length. It usually possesses several mirror planes of symmetry and several twofold axes.
4. The unit cell in which the top face is partially sheared relative to the bottom face and in a direction parallel to one of the box edges is known as_______
a) Orthorhombic unit cell
b) Monoclinic unit cell
c) Triclinic unit cell
d) Trigon unit cell
Explanation: The monoclinic unit cell can be regarded as derived from orthorhombic shoebox by a shearing action in which the top face is partially sheared relative to the bottom face and in a direction parallel tone of the box edges, one of the angles departs from 90˚ and most of the symmetry is lost, apart from a mirror plane and/or a single twofold axis.
5. For the crystal structures how many numbers of Bravais lattice are there?
Explanation: The combination of the crystal system and lattice type gives the Bravais lattice of a structure, there are fourteen possible Bravais lattices. They can be deduced from by taking different allowed combinations of crystal system and space lattice e.g. monoclinic, C-centered monoclinic and primitive triclinic are three of the fourteen possible Bravais lattices.
6. Lattice planes which are introduced with Bragg’s Law are defined from which of the following factors?
a) Shape and concentration of the crystal
b) Solubility and concentration of the crystal
c) Number of unit cell present in the crystal
d) Shape and dimensions of the unit cell of the crystal
Explanation: Bragg’s Law is used to introduce the lattice planes which are defined purely from the shape and the dimensions of the unit cell. Lattice planes are entirely imaginary and simply provide a reference grid to which the atoms in the crystal structure may be referred.
7. Labelling of the lattice planes is done by using ___________
a) Bragg’s indices
b) Miller indices
c) Stockbarger indices
d) Dalton’s indices
Explanation: The lattice planes are labelled by assigning three numbers known as Miller indices to each set. The origin of the unit cell is at O and two planes are shown which are parallel and pass obliquely through the unit cell.
8. In the diffraction of X-rays by the set of a plane, in some cases the resultant intensity is zero, these are caused by absent reflections, what is the number absent reflection is divided?
Explanation: These absent reflection is divided into two groups, first those that are absent due to some quirk in the structure and second those that are absent due to the symmetry or type of lattice possessed by the structure. The latter are known as systematic absences.
9. What is the value of Z (no. of the atoms) in the α-Fe structure?
Explanation: In the α-Fe structure there are corner atoms present which contributes 1/8 thus giving (8 x 1/8=1) and a boy centered atom present in the center of the body. Hence, there are 2 atoms per unit cell in this structure.
10. Which of the following statements is true for the diffraction patterns in the crystal lattice?
a) Diffraction patterns possess a center of symmetry
b) Diffraction patterns doesn’t have center of symmetry
c) Diffraction patterns are linear space
d) Diffraction patterns contains α-rays
Explanation: The diffraction patterns in reciprocal space possess a center of symmetry. This grandiose statement means that miller indices positive hkl and negative hkl reflections are equivalent, subject to the condition that anomalous dispersion is not present.
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