Type of solid and Their properties Questions in English

(B) $NaCl$ is an ionic crystal,therefore it is formed by the electrostatic attraction between $Na^{+}$ and $Cl^{-}$ ions.

(A) In a $CH_4$ molecule,there exists a strong covalent bond between the atoms of each methane molecule.
However,in solid $CH_4$,there exist weak van der Waals' forces between different methane molecules,which is a characteristic of a molecular solid.
Therefore,$CH_4$ is a molecular solid.

(A) Semiconductors like $Si$ or $Ge$ form a crystal lattice through $covalent$ $bonds$.
$n$-type semiconductors are formed by doping with pentavalent impurities (atoms with $5$ valence electrons),which provide extra electrons.
$p$-type semiconductors are formed by doping with trivalent impurities (atoms with $3$ valence electrons),which create electron deficiencies or "holes".
In both cases,the doping atoms substitute for the host atoms in the lattice and participate in the formation of $covalent$ $bonds$ with neighboring atoms.

(B) During the melting of a crystal lattice,the structure of the solid changes.
Because of the repeating geometric arrangement of particles in a crystal,all bonds between the particles have equal strength.
As heat is applied,the energy overcomes the intermolecular forces,causing the rigid lattice structure to break down and transition into a liquid state.

(A) The fusion temperature of naphthalene is the lowest among the given options.
Naphthalene is a non-polar covalent molecular solid held together by weak van der Waals forces.
In contrast,$Diamond$ is a covalent network solid,$NaCl$ is an ionic solid,and $Mn$ is a metallic solid,all of which have significantly stronger inter-particle forces and higher melting points.

(A) The correct answer is $(A)$.
$Ga$ (Gallium) is one of the few substances that expands upon solidification,similar to water.
This behavior is due to the unique crystal structure of $Ga$ in the solid state,which involves weak metallic bonding and the formation of $Ga_2$ molecules,leading to a lower density in the solid phase compared to the liquid phase.

(D) Crystalline metal can be transformed into a metallic glass by very rapid cooling of molten metal.
Rapid cooling of molten metal prevents the atoms from arranging themselves into a regular crystalline lattice,resulting in an amorphous solid known as metallic glass.

(C) The windscreen of automobiles is made up of $Safety \ glass$.
$Safety \ glass$ is a type of glass that is processed by thermal or chemical treatments to increase its strength compared to normal glass.
It is designed to shatter into small,blunt pieces rather than sharp shards when broken,making it less likely to cause injury,which is essential for automotive safety.

(A) Flint glass is used in making optical lenses and prisms.
Flint glass is an optical glass that possesses a relatively high refractive index and a low Abbe number.
$A$ concave lens made of flint glass is commonly combined with a convex lens made of crown glass to produce an achromatic doublet lens.
This combination is used because of their compensating optical properties,which effectively reduce chromatic aberration.

(B) Glass is considered a supercooled liquid because it possesses a disordered,amorphous structure similar to a liquid,but it has a very high viscosity that prevents it from flowing at room temperature.
Supercooling is a process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid.

(B) The correct answer is $B$.
Grey tin ($\alpha$-tin) is very brittle and easily crumbles into a powder in very cold climates.
The transformation is: $\text{Grey tin (Cubic)} \rightleftharpoons \text{White tin (Tetragonal)}$.
The change of white tin to grey tin is accompanied by an increase in volume,which causes the buttons to crumble. This phenomenon is known as $\text{tin disease}$ or $\text{tin plague}$.

(B) Crooke's glass is a special type of glass containing cerium oxide. It does not allow the passage of ultraviolet rays and is used for making lenses.

(B) Polymorphism is the ability of a substance to exist in two or more different crystalline forms or structures.

(C) $Quartz$ is a crystalline variety of $Silica$ $(SiO_2)$.

(A) In $CH_4$ molecules,there exist strong covalent bonds between the atoms within each molecule.
However,in solid $CH_4$,the molecules are held together by weak van der Waals forces.
Since the constituent particles are molecules held by weak intermolecular forces,it is classified as a molecular solid.
Therefore,option $A$ is the correct answer.

(D) Naphthalene $(C_{10}H_8)$ is a molecular solid.
In molecular solids,the constituent particles are molecules.
Naphthalene consists of non-polar molecules held together by weak London dispersion forces (van der Waals forces).
Therefore,it is classified as a molecular solid.

(B) The described phenomenon is a characteristic property of $Liquid \ crystals$.
When heated,these substances pass through an intermediate phase known as the mesomorphic phase,which appears turbid due to the scattering of light by ordered molecular domains.
Upon further heating,the substance transitions into an isotropic liquid state where the turbidity disappears.

(A) $BaTiO_3$ (Barium titanate) is a well-known ferroelectric compound.
In ferroelectric substances,the dipoles are permanently aligned in the same direction even in the absence of an electric field.

(A) $1.$ Molecular crystals are substances that have relatively weak intermolecular binding forces.
$2.$ These crystals are soft and have low melting points.
$3.$ They are poor conductors of heat and electricity.
$4.$ Solid carbon dioxide $(CO_2)$ is commonly known as dry ice.
$5.$ The constituent particles in solid $CO_2$ are molecules held together by weak intermolecular forces (van der Waals forces).
Therefore,solid $CO_2$ is an example of a molecular crystal.

(B) The value of the heat of fusion of $NaCl$ is very high because it is an ionic solid with a strong electrostatic force of attraction between its ions in an $fcc$ crystal lattice structure.

(C) Piezoelectric crystals are materials that produce an electric potential when mechanical stress is applied to them.
They are commonly used in devices like record players (pickups),microphones,and ultrasonic generators.
Therefore,the correct option is $C$.

(B) $NaCl$ is an ionic solid in which constituent particles are positive $(Na^{+})$ and negative $(Cl^{-})$ ions.

(D) Amorphous solids possess only short-range order in the arrangement of their constituent particles.
They do not have a sharp melting point,meaning they soften over a range of temperatures.
Therefore,statements $B$ and $D$ are correct.

(D) Solids are characterized by strong intermolecular forces that hold their constituent particles in fixed positions.
Consequently,they possess a definite shape,a definite volume (size),and high rigidity.

(A) Crystalline solids are characterized by a long-range order of constituent particles and possess a sharp,definite melting point.
When heated,they undergo a phase transition from solid to liquid at a specific temperature,which is why they change abruptly from solid to liquid.

(C) Diamond is a covalent solid (network solid) in which carbon atoms are linked by strong covalent bonds in a three-dimensional tetrahedral structure.

(A) Solids can be classified into two types: crystalline and amorphous.
Therefore,the statement that solids are always crystalline in nature is incorrect,as amorphous solids also exist.

(C) Metallic solids consist of positive metal ions surrounded by a sea of delocalized electrons.
$W$ (Tungsten) is a metal and forms a metallic crystalline solid.
$C$ (Diamond/Graphite) is a covalent network solid.
$Si$ (Silicon) is a covalent network solid.
$AgCl$ is an ionic solid.

(C) $I_2$ crystals are molecular crystals.
In these crystals,the constituent particles are $I_2$ molecules.
The molecules are held together by weak $Van \text{ } der \text{ } Waals$ forces.

(B) $ (b) $ Ionic solids have the highest melting point due to strong electrostatic forces of attraction between the oppositely charged ions.

(D) Silicon is a group $14$ element with $4$ valence electrons.
To obtain an $n-$type semiconductor,we need to dope silicon with an element having more valence electrons than silicon.
Elements of group $15$ have $5$ valence electrons.
Therefore,adding an impurity with $5$ valence electrons creates an $n-$type semiconductor due to the presence of extra electrons.

(D) $Glass$ is an amorphous solid,which means it lacks a long-range ordered arrangement of its constituent particles. In contrast,$CsCl$,$NaCl$,and $CaF_2$ are crystalline solids with a regular,repeating pattern.

(A) Crystalline solids are characterized by a regular,repeating pattern of constituent particles extending throughout the entire crystal lattice,which is known as long-range order.
In contrast,amorphous solids exhibit only short-range order.

(D) Sugar is a crystalline solid,while glass,rubber,and plastic are amorphous solids.

(A) Antiferromagnetic substances possess equal number of parallel and anti-parallel magnetic moments,resulting in a net magnetic moment of zero.
Among the given options,$MnO_2$ exhibits antiferromagnetic behavior.
$TiO_2$ is diamagnetic,while $VO_2$ and $CrO_2$ are ferromagnetic.

(D) $Ice$ is a molecular crystal in which the constituent units are molecules and the interparticle forces are hydrogen bonds.

(A) Quartz is a crystalline form of silica $(SiO_2)$.
It is a covalent network solid where each silicon atom is bonded to four oxygen atoms in a tetrahedral arrangement,and each oxygen atom is shared between two silicon atoms,forming a three-dimensional network.

(C) Metallic crystals are good conductors of heat and electricity due to the presence of free electrons within their structure.

(A) $Si$ (Silicon) is a covalent network solid (also known as a covalent crystal) in which the constituent particles are atoms linked by a continuous network of covalent bonds.

(B) $LiF$ is an example of an ionic crystal solid,in which the constituent particles are positive $(Li^{+})$ and negative $(F^{-})$ ions held together by strong electrostatic forces of attraction.

(A) Amorphous solids do not have a long-range ordered arrangement of particles,meaning they lack a definite geometric shape and a sharp melting point.
When heated,they gradually soften over a range of temperatures until they behave like liquids.
Therefore,they are often referred to as super-cooled liquids.
Glass is a classic example of an amorphous solid,whereas $NaCl$,$CsCl$,and $CaF_2$ are crystalline solids.

(A) Silicon is a semiconductor because it is thermally active and its conductivity increases with increasing temperature.

(B) The correct answer is $(B)$. Amorphous solids are isotropic,meaning they exhibit the same physical properties in all directions. In contrast,crystalline solids are anisotropic.

(C) The ability of a substance to exist in two or more different crystalline forms is known as $Polymorphism$.
For example,$CaCO_3$ exists as calcite and aragonite.

(D) Amorphous solids do not have a long-range ordered arrangement of particles,nor do they have a sharp melting point like crystalline solids.
When heated,they gradually soften and become pliable,eventually exhibiting properties associated with liquids.
Because of this property of flowing very slowly over long periods,glass is often regarded as a supercooled liquid.

(B) In a crystal lattice,atoms arrange themselves in a configuration that minimizes the total potential energy $(P.E.)$ of the system.
This state of minimum potential energy corresponds to the most stable arrangement of particles.

(C) When a polar crystal is subjected to mechanical stress,electricity is produced; this phenomenon is known as piezoelectricity.
Conversely,if an electric field is applied to such crystals,mechanical stress is developed.
Thus,a piezoelectric crystal acts as a mechanical-electrical transducer.

(D) Silicon $(Si)$ belongs to group $14$ of the periodic table,while boron $(B)$ belongs to group $13$.
When silicon is doped with boron,boron atoms occupy some lattice sites of silicon.
Since boron has only $3$ valence electrons,it creates an electron deficiency or a 'hole' in the crystal lattice.
This electron-deficient site acts as a positive charge carrier,resulting in the formation of a $p$-type semiconductor.

(B) When small non-metal atoms (like $H$,$C$,$N$) occupy the interstitial sites of a metal crystal lattice,they hinder the movement of metal layers over each other. This makes the metal harder and less tensile.

(B) Brass is a substitutional alloy because $Zn$ atoms replace $Cu$ atoms in the crystal lattice.
Steel is an interstitial alloy because it is an alloy of $Fe$ with $C$,where small $C$ atoms occupy the interstitial voids of the $Fe$ crystal lattice.