Each question consists of an assertion (A) and a reason (R). You need to select the correct option based on the given statements:
Assertion (A): Crystalline solids are anisotropic in nature.
Reason (R): Crystalline solids have long-range order, and their
physical properties vary with direction.
Answer: 1
Explanation: Crystalline solids exhibit anisotropy because
their properties depend on the orientation of the crystal lattice due to its
long-range order.
Assertion (A): Amorphous solids are sometimes called
pseudo-solids.
Reason (R): Amorphous solids possess a definite melting point.
Answer: 3
Explanation: Amorphous solids are pseudo-solids because they do
not have a definite melting point; instead, they melt over a range of
temperatures.
Assertion (A): Ionic solids have high melting points.
Reason (R): Strong electrostatic forces of attraction exist
between oppositely charged ions in ionic solids.
Answer: 1
Explanation: Ionic solids have high melting points because
significant energy is required to overcome the strong electrostatic forces
between ions.
Assertion (A): Covalent solids like diamond are hard and
brittle.
Reason (R): Covalent solids consist of atoms connected through
covalent bonds throughout the crystal.
Answer: 2
Explanation: While diamond is extremely hard due to its
covalent bonds, brittleness is not necessarily related to its bonding nature.
Assertion (A): Metallic solids are good conductors of
electricity.
Reason (R): In metallic solids, electrons are localized between
metal ions.
Answer: 4
Explanation: Metallic solids have delocalized electrons, not
localized ones, which facilitate the conduction of electricity.
Assertion (A): Molecular solids have low melting and boiling
points.
Reason (R): Intermolecular forces in molecular solids are weak
van der Waals forces or hydrogen bonds.
Answer: 1
Explanation: The low melting and boiling points of molecular
solids are due to weak intermolecular forces.
Assertion (A): Graphite is a good conductor of electricity.
Reason (R): Graphite has free electrons within its layers.
Answer: 1
Explanation: Graphite conducts electricity due to the presence
of delocalized π-electrons in its planar layers.
Assertion (A): Solids have definite shape and volume.
Reason (R): The intermolecular forces in solids are weak.
Answer: 3
Explanation: Solids have definite shape and volume because
their intermolecular forces are strong, not weak.
Assertion (A): Ionic solids are brittle.
Reason (R): Ionic solids have strong covalent bonds.
Answer: 3
Explanation: Ionic solids are brittle because displacement of
ions causes repulsion between like charges, but the bonds are ionic, not
covalent.
Assertion (A): The packing efficiency of hcp and ccp
arrangements is the same.
Reason (R): Both hcp and ccp arrangements have a coordination
number of 12.
Answer: 1
Explanation: Both hcp and ccp arrangements achieve a packing
efficiency of 74% due to their identical coordination numbers and space
utilization.
Assertion (A): Frenkel defects do not affect the density of the
solid.
Reason (R): In Frenkel defects, ions are displaced within the
crystal lattice.
Answer: 1
Explanation: Since no ions are removed from the lattice in
Frenkel defects, the overall density remains unchanged.
Assertion (A): Schottky defects reduce the density of a
crystal.
Reason (R): Schottky defects involve the removal of ions from
the lattice, leaving vacancies.
Answer: 1
Explanation: In Schottky defects, equal numbers of cations and
anions are missing, reducing the mass per unit volume.
Assertion (A): Ionic solids are soluble in polar solvents.
Reason (R): Polar solvents stabilize ions through ion-dipole
interactions.
Answer: 1
Explanation: The polarity of solvents helps dissolve ionic
solids by stabilizing separated ions.
Assertion (A): NaCl exhibits a Schottky defect.
Reason (R): NaCl has a small difference in the size of its
cation and anion.
Answer: 1
Explanation: NaCl, with cations and anions of similar size,
typically exhibits Schottky defects.
Assertion (A): ZnO is white when cold but yellow when hot.
Reason (R): Heating ZnO generates free electrons due to the
loss of oxygen.
Answer: 1
Explanation: The yellow color arises because free electrons
generated at high temperatures absorb certain wavelengths of light.
Assertion (A): The coordination number of Na+ in NaCl is 6.
Reason (R): NaCl has a cubic close-packed structure.
Answer: 1
Explanation: In NaCl, each Na+ is surrounded by six Cl− ions
due to its ccp arrangement.
Assertion (A): The void space in a simple cubic lattice is 32%.
Reason (R): The packing efficiency of a simple cubic lattice is
68%.
Answer: 4
Explanation: The packing efficiency of a simple cubic lattice
is 52%, not 68%, and the void space is 48%.
Assertion (A): All solids are crystalline in nature.
Reason (R): Solids have regular arrangements of particles.
Answer: 4
Explanation: Some solids, like amorphous solids, do not have a
regular arrangement of particles.
Assertion (A): Covalent solids are poor conductors of
electricity.
Reason (R): Covalent bonds involve localized electrons.
Answer: 1
Explanation: The absence of free electrons or ions in covalent
solids prevents electrical conductivity.
Assertion (A): Silicon doped with phosphorus is a p-type
semiconductor.
Reason (R): Phosphorus contributes extra electrons to the
silicon lattice.
Answer: 4
Explanation: Phosphorus doping results in an n-type
semiconductor because it provides extra electrons.
Assertion (A): The number of atoms per unit cell in a bcc
lattice is 4.
Reason (R): The bcc lattice has one atom at the center and
eight at the corners.
Answer: 3
Explanation: The number of atoms per unit cell in a bcc lattice
is 2, not 4.
Assertion (A): The unit cell of a hexagonal close-packed
structure has six atoms.
Reason (R): The hcp structure has an ABAB type of arrangement.
Answer: 1
Explanation: The hcp unit cell contains six atoms and exhibits
an ABAB pattern.
Assertion (A): Diamond has a high melting point.
Reason (R): Diamond consists of covalent bonds extending
throughout the structure.
Answer: 1
Explanation: Diamond's strong covalent bonding throughout the
lattice gives it a high melting point.
Assertion (A): Glass is an amorphous solid.
Reason (R): Glass has a long-range order of particles.
Answer: 3
Explanation: Glass lacks long-range order, making it an
amorphous solid.
Assertion (A): Ionic solids are good conductors of electricity
in the solid state.
Reason (R): Ionic solids have free ions in the solid state.
Answer: 4
Explanation: Ionic solids do not conduct electricity in the
solid state because ions are not free to move.
Assertion (A): In a face-centered cubic (fcc) lattice, the
packing efficiency is 74%.
Reason (R): The coordination number in fcc lattices is 12.
Answer: 1
Explanation: The high packing efficiency of fcc lattices is due
to the close packing and coordination number of 12.
Assertion (A): CsCl and NaCl have the same type of crystal
structure.
Reason (R): Both CsCl and NaCl are ionic compounds.
Answer: 4
Explanation: CsCl has a bcc structure, while NaCl has a ccp
structure.
Assertion (A): Metals are malleable and ductile.
Reason (R): Metallic bonds are non-directional.
Answer: 1
Explanation: The non-directional nature of metallic bonds
allows metals to deform without breaking.
Assertion (A): Crystalline solids have sharp melting points.
Reason (R): Crystalline solids have a regular arrangement of
particles.
Answer: 1
Explanation: Sharp melting points result from the uniformity of
the crystal lattice.
Assertion (A): Quartz is an example of an amorphous solid.
Reason (R): Quartz has a regular three-dimensional arrangement
of particles.
Answer: 4
Explanation: Quartz is a crystalline solid due to its
long-range ordered structure.
Assertion (A): A crystal with a point defect always loses its
electrical neutrality.
Reason (R): Point defects disrupt the overall balance of
positive and negative charges.
Answer: 4
Explanation: Electrical neutrality is maintained in most point
defects like Frenkel and Schottky defects.
Assertion (A): The packing efficiency of a simple cubic lattice
is lower than that of a body-centered cubic lattice.
Reason (R): The atoms in a body-centered cubic lattice are more
closely packed than in a simple cubic lattice.
Answer: 1
Explanation: The packing efficiency of a bcc lattice (68%) is
greater than that of a simple cubic lattice (52%).
Assertion (A): Amorphous solids are isotropic.
Reason (R): Amorphous solids have no long-range order in their
structure.
Answer: 1
Explanation: Isotropy in amorphous solids results from the
random arrangement of particles, making properties uniform in all directions.
Assertion (A): Ionic solids in molten state conduct
electricity.
Reason (R): Ionic solids in molten state have free ions that
move under an electric field.
Answer: 1
Explanation: Free ions in the molten state facilitate
electrical conductivity.
Assertion (A): Silicon is used as a semiconductor.
Reason (R): Silicon has a diamond-like covalent structure with
a small energy gap between valence and conduction bands.
Answer: 1
Explanation: The small energy gap allows silicon to behave as a
semiconductor.
Assertion (A): Graphite is used as a lubricant.
Reason (R): Graphite has a layered structure with weak van der
Waals forces between the layers.
Answer: 1
Explanation: The layers in graphite can slide over each other,
making it an effective lubricant.
Assertion (A): Non-stoichiometric defects can lead to color in
solids.
Reason (R): Non-stoichiometric defects produce free electrons
or electron holes that absorb specific wavelengths of light.
Answer: 1
Explanation: Non-stoichiometric defects can cause color changes
due to electronic transitions.
Assertion (A): Crystalline solids are generally incompressible.
Reason (R): In crystalline solids, particles are closely
packed, leaving no space for compression.
Answer: 1
Explanation: The tightly packed structure of crystalline solids
makes them incompressible.
Assertion (A): In a face-centered cubic lattice, each atom
touches four other atoms.
Reason (R): In a face-centered cubic lattice, the coordination
number is 12.
Answer: 3
Explanation: In an fcc lattice, each atom touches 12 other
atoms, not 4.
Assertion (A): Molecular solids like ice have low melting
points.
Reason (R): Molecular solids are held together by strong
covalent bonds.
Answer: 3
Explanation: Molecular solids are held together by weak
intermolecular forces, not covalent bonds.
Assertion (A): An interstitial defect increases the density of
a crystal.
Reason (R): Interstitial defects occur when extra atoms occupy
positions in the voids of the crystal lattice.
Answer: 1
Explanation: Adding atoms to the voids increases the mass
without changing the volume significantly, increasing density.
Assertion (A): In Frenkel defect, there is no change in the
electrical neutrality of the compound.
Reason (R): In Frenkel defect, ions simply shift from their
lattice points to interstitial sites.
Answer: 1
Explanation: No ions are lost; they are displaced, maintaining
electrical neutrality.
Assertion (A): The coordination number of an atom in a simple
cubic lattice is 8.
Reason (R): In a simple cubic lattice, each atom is in contact
with 8 other atoms.
Answer: 4
Explanation: The coordination number in a simple cubic lattice
is 6, not 8.
Assertion (A): The electrical conductivity of semiconductors
increases with an increase in temperature.
Reason (R): Heating provides energy for more electrons to jump
into the conduction band.
Answer: 1
Explanation: At higher temperatures, electrons gain energy to
move to the conduction band, increasing conductivity.
Assertion (A): All crystalline solids are anisotropic.
Reason (R): Anisotropy arises due to a regular arrangement of
particles in different directions in a crystal.
Answer: 1
Explanation: The direction-dependent properties of crystalline
solids result from their lattice arrangement.
Assertion (A): The number of atoms in a unit cell of a cubic
close-packed structure is 4.
Reason (R): In a cubic close-packed structure, atoms are
present at the corners and face centers.
Answer: 1
Explanation: The calculation of atoms in an fcc unit cell gives
4 atoms per unit cell.
Assertion (A): Impurities in semiconductors alter their
electrical conductivity.
Reason (R): Impurities create additional energy levels in the
semiconductor.
Answer: 1
Explanation: Impurity levels enhance conductivity by allowing
more charge carriers to participate.
Assertion (A): NaCl is a good conductor in the solid state.
Reason (R): Ionic mobility in NaCl is high in the solid state.
Answer: 4
Explanation: NaCl is not a conductor in the solid state due to
the immobility of ions.
Assertion (A): Diamond and graphite are allotropes of carbon.
Reason (R): Diamond has a layered structure, while graphite has
a three-dimensional network.
Answer: 3
Explanation: Diamond has a 3D network structure, while graphite
has a layered structure.
Assertion (A): The packing efficiency of hexagonal close
packing is higher than that of a simple cubic lattice.
Reason (R): Hexagonal close packing utilizes space more
efficiently than a simple cubic lattice.
Answer: 1
Explanation: Hexagonal close packing achieves 74% packing
efficiency, compared to 52% for a simple cubic lattice.