Type of solid and Their properties Questions in English

(N/A) $Quartz$ is extensively used as a piezoelectric material. It has made it possible to develop extremely accurate clocks,modern radio and television broadcasting,and mobile radio communications.

(B) When glass is heated,it softens and melts into a liquid state. Due to surface tension,the liquid glass tends to minimize its surface area,causing sharp edges to become rounded. This process of heating glass to round off sharp edges is known as $Fire \ Polishing$ of glass.

(N/A) If we measure the thickness of glass panes in old buildings,they are found to be slightly thicker at the bottom than at the top.
This observation proves that glass is a supercooled liquid,which flows very slowly from top to bottom over a long period of time.

(A) Materials are classified into conductors,insulators,and semiconductors based on the magnitude of their electrical conductivity.
$1$. Conductors: These materials have very high conductivity. Examples include metals and their alloys (e.g.,$Na, Cu, Ag, Au, Fe$),certain non-metals like carbon black and graphite,and some electronically conducting organic polymers.
$2$. Insulators: These materials have very low conductivity. Examples include glass,ceramics,and polymers like Teflon.
$3$. Semiconductors: These materials have conductivity values between those of conductors and insulators. Examples include silicon,doped silicon,gallium arsenide,and certain oxides like $CuO$. These are important electronic materials.
$4$. Superconductors: These are materials that exhibit zero resistivity or infinite conductivity. While earlier only metals and alloys at very low temperatures ($0 \ K$ to $15 \ K$) were known to be superconductors,many ceramic materials and mixed oxides are now known to exhibit superconductivity at temperatures as high as $150 \ K$.

(N/A) The classification is as follows:
$1$. Conductors: $Cu$,$Al$,$Au$,$Pt$,graphite,carbon black.
$2$. Semiconductors: $Si$,$Ge$.
$3$. Insulators: glass,Teflon.
$4$. Superconductors: $CuO$ (at low temperature),alloys at low temperature.

(C) Diamond is a giant molecule in which constituent atoms are held together by covalent bonds. Hence,it is a network solid.
$SO_{2}$ (solid),$H_{2}O$ (ice),and $I_{2}$ are examples of molecular solids.

(D) $MnO$ is antiferromagnetic because the magnetic moments of the domains are aligned in a compensatory manner,resulting in a net magnetic moment of zero. This is illustrated by the alternating spin directions shown below:
(Image shows a grid of arrows pointing up and down in an alternating pattern,labeled as Antiferromagnetic).

(D) Covalent or network solids possess a giant three-dimensional structure held together by strong covalent bonds,which results in a very high melting point.
Since all electrons are involved in bonding and are not free to move,these substances act as insulators in both their solid and molten states.

(C) The magnetic properties of substances are classified as follows:
$a$. Diamagnetism: Substances that are weakly repelled by a magnetic field,e.g.,$NaCl$ (all electrons are paired).
$b$. Ferrimagnetism: Substances where magnetic moments are aligned in parallel and anti-parallel directions in unequal numbers,e.g.,$Fe_{3}O_{4}$.
$c$. Paramagnetism: Substances that are weakly attracted by a magnetic field due to the presence of unpaired electrons,e.g.,$O_{2}$.
$d$. Antiferromagnetism: Substances where magnetic moments are aligned in a compensatory way such that the net magnetic moment is zero,e.g.,$MnO$.
Therefore,the correct matching is: $a-iii, b-iv, c-ii, d-i$.

(D) Glass is an amorphous solid. On heating,it softens and flows,which causes the sharp edges to become smooth due to surface tension.
Assertion $A$ is true because heating glass to its melting point allows it to flow and round off sharp edges.
Reason $R$ is true because the viscosity of glass decreases as temperature increases,allowing it to flow more easily.
However,the smoothing of edges is primarily due to the effect of surface tension,not just the decrease in viscosity. Therefore,$R$ is not the correct explanation for $A$.

(B) Crystalline solids have a regular,repeating arrangement of constituent particles and exhibit long-range order.
$(B)$ Crystalline solids are anisotropic,meaning their physical properties vary with direction.
$(C)$ Amorphous solids are often referred to as pseudo solids or supercooled liquids because they lack a long-range ordered structure.
$(D)$ Amorphous solids do not have a sharp melting point; they gradually soften over a range of temperatures.
$(E)$ Amorphous solids do not have a definite heat of fusion because they do not have a sharp melting point.
Therefore,statements $(A)$,$(C)$,and $(D)$ are correct.

(N/A) When a substance possesses different magnitudes of physical properties such as electrical conductivity,refractive index,and thermal expansion along different directions,it is said to be anisotropic,and this property is known as anisotropy.
Anisotropy in crystals is due to the different arrangement of particles along different directions. The figure shows a simple two-dimensional pattern of the arrangement of two kinds of atoms. $A$ mechanical property such as resistance to shearing stress might be quite different in two directions $AB$ and $CD$. Deformation in the $CD$ direction displaces a row which has two different types of atoms,while in the $AB$ direction,rows made of one type of atoms are displaced.

(N/A) Crystalline solids are classified based on the nature of the intermolecular forces or bonds that hold the constituent particles together.
These are classified into four main categories:
$(i)$ Ionic solids: Held together by strong electrostatic forces of attraction between ions (e.g.,$NaCl$,$ZnS$).
$(ii)$ Covalent (Network) solids: Held together by covalent bonds forming a continuous network (e.g.,$SiO_2$,diamond,graphite).
$(iii)$ Metallic solids: Held together by metallic bonds involving a sea of delocalized electrons (e.g.,$Fe$,$Cu$,$Ag$).
$(iv)$ Molecular solids: Held together by Van der Waals forces or hydrogen bonds (e.g.,$I_2$,$P_4$,$H_2O$).
In graphite,the presence of free electrons makes it a good conductor of electricity.

(N/A) Solids exhibit electrical conductivities ranging from $10^{-20}$ to $10^{7} \ \Omega^{-1} \ m^{-1}$. They are classified into three categories:
$(i)$ Conductors: Solids with conductivities ranging between $10^{4}$ to $10^{7} \ \Omega^{-1} \ m^{-1}$. Metals have conductivities in the order of $10^{7} \ \Omega^{-1} \ m^{-1}$ and are good conductors.
$(ii)$ Insulators: Solids with very low conductivities ranging between $10^{-20}$ to $10^{-10} \ \Omega^{-1} \ m^{-1}$. Examples include wood and plastics.
$(iii)$ Semiconductors: Solids with conductivities in the intermediate range from $10^{-6}$ to $10^{4} \ \Omega^{-1} \ m^{-1}$. Their conductivity is mainly due to defects or impurities. The conduction of electricity in metals and semiconductors is explained by Band Theory.
Certain transition metal oxides show variations in electrical properties:

Electrical Property	Transition Metal Oxides
Metals-like oxides	$TiO, CrO_{2}, ReO_{3}, VO$
Metal-to-insulator behavior at certain temperatures	$Ti_{2}O_{3}, VO_{2}, V_{2}O_{3}$
Insulators-like oxides	$MnO, CuO, FeO$

$ReO_{3}$ has an appearance and conductivity similar to copper.

(N/A) The process of increasing the conductivity of intrinsic semiconductors by adding a small amount of suitable impurities is known as $doping$. The added impurities are called $dopants$.
Doping is performed to modify the electronic properties of semiconductors like $Si$ or $Ge$. Depending on the nature of the impurity,two types of extrinsic semiconductors are formed:
$(i)$ $n$-type semiconductors: Formed by doping with electron-rich impurities (Group $15$ elements like $P$ or $As$ added to Group $14$ elements).
$(ii)$ $p$-type semiconductors: Formed by doping with electron-deficient impurities (Group $13$ elements like $B$ or $Al$ added to Group $14$ elements).

(N/A) $(i)$ $n$-type semiconductors: These semiconductors are obtained by adding electron-rich impurities to silicon or germanium. Silicon and germanium belong to group-$14$ and have four valence electrons each. In their crystals,each atom forms four covalent bonds with its neighbors. When doped with group-$15$ elements like $P$ or $As$,which contain five valence electrons,they occupy some lattice sites in the silicon or germanium crystal. Four out of five electrons are used to form four covalent bonds with four neighboring silicon atoms. The fifth electron is extra and is delocalized. These delocalized electrons increase the conductivity of the doped silicon or germanium,and this increase is due to the negatively charged electron. Hence,silicon doped with an electron-rich impurity is called an $n$-type semiconductor.
$(ii)$ $p$-type semiconductors: These semiconductors are obtained by adding electron-deficient impurities to silicon or germanium. When silicon or germanium is doped with a group-$13$ element such as $B$,$Al$,or $Ga$,which contains only three valence electrons,an electron hole is formed where the fourth electron is missing. This is also known as an electron vacancy or hole. Under an applied electric field,electrons from neighboring atoms can move to fill the hole,effectively moving the hole in the opposite direction. Since the hole behaves as a positive charge,this is called a $p$-type semiconductor.

(N/A) The origin of magnetic properties in a substance is due to two types of motions of electrons:
$(i)$ Orbital motion around the nucleus.
$(ii)$ Spin motion around its own axis.
An electron in an atom behaves like a tiny magnet. Since an electron is a charged particle and undergoes these motions,it can be considered as a small loop of current which possesses a magnetic moment.
Each electron thus has a permanent spin and an orbital magnetic moment associated with it. The magnitude of the magnetic moment is very small and is measured in the unit called Bohr magneton,$\mu_{B}$,which is equal to $9.27 \times 10^{-24} \text{ A m}^{2}$.
On the basis of their magnetic properties,substances are classified as:
$(i)$ Paramagnetic
$(ii)$ Diamagnetic
$(iii)$ Ferromagnetic
$(iv)$ Antiferromagnetic
$(v)$ Ferrimagnetic

(N/A) Ferrimagnetism is observed when the magnetic moments of the domains in a substance are aligned in parallel and anti-parallel directions in unequal numbers.
These substances are weakly attracted by a magnetic field compared to ferromagnetic substances.
Upon heating,these substances lose their ferrimagnetism and become paramagnetic.
Examples include $MgFe_{2}O_{4}$,$Fe_{3}O_{4}$,and $ZnFe_{2}O_{4}$.

(A) $O_2, Cu^{2+}$ and $Fe^{3+}$ contain unpaired electrons,hence they are paramagnetic.
Paramagnetic substances are weakly attracted by an external magnetic field and are magnetized in the direction of the field.
$NaCl$ and $H_2O$ have all electrons paired,hence they are diamagnetic.
Diamagnetic substances are weakly repelled by an external magnetic field and are weakly magnetized in the direction opposite to the applied magnetic field.
Therefore,both Statement $I$ and Statement $II$ are correct.

(B) The characteristics provided describe an $ionic$ $solid$.
$1$. $Ionic$ solids are hard and brittle due to strong electrostatic forces of attraction.
$2$. They act as insulators in the solid state because ions are fixed in their lattice positions.
$3$. They conduct electricity in the molten state or in aqueous solution because the ions become free to move.

(B) Semiconductors are materials with electrical conductivity between conductors and insulators. $Germanium$,$Silicon$,and $Copper \ oxide$ $(Cu_2O)$ are well-known semiconductors. $Graphite$ is an allotrope of carbon that possesses delocalized electrons,making it a good conductor of electricity. Therefore,$Graphite$ is not a semiconductor.

(C) $Statement-1$ is True because Germanium is a semiconductor with a small band gap (approx $0.7 \ eV$).
$Statement-2$ is False. In a solid,atomic energy levels overlap to form energy bands due to the interaction of a large number of atoms,which results in a significant energy spread,not an infinitesimally small one.

(C) $SiO_2$ (silica) has the highest $m.p.$ because it possesses a three-dimensional covalent network structure.
In contrast,$CO_2$ and $He_{(s)}$ are molecular solids held by weak van der Waals forces,and $H_2O$ (ice) is a molecular solid held by hydrogen bonds,all of which have significantly lower melting points than the giant covalent network of $SiO_2$.

(C) Ice is the solid form of water $(H_2O)$.
In ice,water molecules are held together by hydrogen bonding,which is a type of intermolecular force.
Therefore,ice is classified as a molecular solid.

(D) non-polar solid is one that does not possess a permanent dipole moment.
$CO_2$ (Carbon dioxide) has a linear geometry with two $C=O$ bonds oriented at $180^{\circ}$.
The bond dipoles cancel each other out,resulting in a net dipole moment of zero,making it a non-polar molecule.

(C) Isomorphism is the phenomenon where different substances crystallize in the same crystalline form and have similar chemical formulas.
Sodium nitrate $(NaNO_3)$ and calcium carbonate $(CaCO_3)$ are classic examples of isomorphism.
Both crystallize in the rhombohedral system and have similar structural arrangements of their constituent ions.
Calcite and aragonite are polymorphs of $CaCO_3$,not isomorphs.
$ \alpha $-quartz and cristobalite are polymorphs of $SiO_2$.
Diamond and fullerene are allotropes of carbon.

(A) polar molecular solid consists of molecules held together by dipole-dipole interactions.
$CH_{4}$ has a symmetrical tetrahedral geometry,which results in a net dipole moment of $0$.
Therefore,$CH_{4}$ is a non-polar molecular solid.
$SO_{2}$,$HCl$,and $H_{2}S$ are polar molecules due to the difference in electronegativity between the bonded atoms and their non-symmetrical shapes.

(D) Polymorphism is the ability of a solid material to exist in more than one form or crystal structure.
Since these forms have different crystal structures,their physical properties like crystal shape,density,and melting point are different.
Therefore,the statement that the crystal shape of polymorphic substances is identical is false.

(A) Amorphous solids are isotropic in nature,meaning their physical properties (such as refractive index,electrical conductivity,etc.) are the same in all directions.
Glass is an amorphous solid,whereas ceramics,graphite,and ice are crystalline solids,which are anisotropic.

(D) Amorphous solids are isotropic in nature,meaning they exhibit the same magnitude for physical properties like refractive index,electrical conductivity,etc.,in every direction.
Metallic glass is an amorphous solid.
Therefore,it is isotropic in nature.

(B) Crystalline solids are anisotropic in nature,meaning their physical properties such as refractive index,thermal conductivity,and electrical conductivity vary when measured in different directions. Therefore,the statement that a crystalline solid is isotropic is incorrect.

(D) Crystalline solids are anisotropic in nature,meaning they exhibit different physical properties (such as refractive index) when measured in different directions. Therefore,the statement that they are isotropic is incorrect.

(D) Diamond is a crystalline solid because its constituent particles are arranged in a regular,repeating pattern throughout the entire structure.
In contrast,glass,plastic,and rubber are amorphous solids because they lack a long-range ordered arrangement of particles.

(A) Polymorphism refers to the ability of a solid material to exist in more than one form or crystal structure.
$NaF$ and $MgO$ both crystallize in the rock salt structure ($NaCl$ type) and do not exhibit polymorphism.
Therefore,the statement that $NaF$ and $MgO$ are polymorphous compounds is incorrect.

(D) Covalent network solids,also known as giant molecules,are formed by a continuous network of covalent bonds throughout the crystal. Due to this strong,directional bonding,they are extremely hard and have very high melting points. Therefore,the statement that they are soft in nature is incorrect.

(D) Amorphous solids are those in which the constituent particles do not have a long-range order of arrangement.
$Glass$,$rubber$,and $plastics$ are common examples of amorphous solids.
$Camphor$ is a crystalline molecular solid.
$Magnesium$ is a metallic crystalline solid.
$Diamond$ is a covalent (network) crystalline solid.
Therefore,$Glass$ is the correct example of an amorphous solid.

(D) Amorphous solids are those in which the constituent particles do not have a long-range ordered arrangement. Examples include rubber,glass,plastic,and tar.
Crystalline solids have a long-range ordered arrangement of constituent particles. Camphor is a molecular crystalline solid.
Therefore,camphor is $NOT$ an amorphous solid.

(B) Silica $(SiO_2)$ is a covalent solid (also known as a network solid).
In this structure,silicon and oxygen atoms are held together by strong covalent bonds in a continuous three-dimensional network.
This extensive bonding results in high hardness and a very high melting point for silica.

(A) Polonium $(Po)$ is the only known metal that crystallizes in a simple cubic structure.

(A) Polonium $(Po)$ is the only known metal that crystallizes in a simple cubic structure at room temperature.

(A) $CaF_2$ is an ionic solid.
$Ice$ is a molecular solid.
$SiO_2$ is a covalent network (atomic) solid.
$Na$ is a metallic solid.

(D) Ionic solids consist of ions held together by strong electrostatic forces of attraction,making them hard and brittle. However,in the solid state,the ions are fixed in their lattice positions and are not free to move. Therefore,they are poor conductors of electricity in the solid state. They only conduct electricity when molten or dissolved in water,as the ions become free to move. Thus,statement $D$ is incorrect.

(A) To form an $n-$type semiconductor,a pentavalent impurity (Group $15$ element) is added to a tetravalent semiconductor like germanium $(Ge)$.
Among the given options,$As$ (Arsenic) is a Group $15$ element,while $B$ (Boron),$In$ (Indium),and $Ga$ (Gallium) are Group $13$ elements.
Adding a Group $15$ element provides an extra electron,which is responsible for $n-$type conductivity.
Therefore,$As$ is the correct dopant.

(A) To produce a $p-$type semiconductor,a group $13$ element (trivalent impurity) is added to a group $14$ element like germanium.
$B$ (Boron) belongs to group $13$,while $P$ (Phosphorus),$As$ (Arsenic),and $Sb$ (Antimony) belong to group $15$ (pentavalent impurities).
Adding a group $13$ element creates an electron hole,which is responsible for $p-$type conductivity.
Therefore,$B$ is the correct dopant.

(A) To produce a $p$-type semiconductor, silicon (a group $14$ element) is doped with a group $13$ element.
Group $13$ elements have $3$ valence electrons, which create an electron deficiency or 'hole' in the crystal lattice.
Among the given options, $Ga$ (Gallium) belongs to group $13$, while $Sb$ (Antimony), $As$ (Arsenic), and $P$ (Phosphorus) belong to group $15$.
Group $15$ elements are used to produce $n$-type semiconductors.
Therefore, $Ga$ is the correct dopant.

(A) To obtain an $n$-type semiconductor, a group-$15$ element (pentavalent) is added as a dopant to a group-$14$ element like silicon $(Si)$.
Among the given options, $As$ (Arsenic) belongs to group-$15$, while $B$ (Boron), $Ga$ (Gallium), and $In$ (Indium) belong to group-$13$.
Therefore, adding $As$ to $Si$ creates an $n$-type semiconductor due to the presence of an extra electron.

(C) The magnetic properties of the given substances are as follows:
$1$. $NaCl$: Diamagnetic
$2$. $C_6H_6$: Diamagnetic
$3$. $CrO_2$: Ferromagnetic
$4$. $H_2O$: Diamagnetic
Therefore,$CrO_2$ is the ferromagnetic substance.

(A) An $n$-type semiconductor is formed when a group $14$ element (like silicon or germanium) is doped with a group $15$ element (like phosphorus or arsenic) that has more valence electrons.
$(1)$ Silicon has $4$ valence electrons. Phosphorus has $5$ valence electrons.
$(2)$ When silicon is doped with phosphorus,$4$ electrons of phosphorus form covalent bonds with silicon,while the $5^{th}$ electron remains free.
$(3)$ This extra free electron increases the electrical conductivity,resulting in an $n$-type semiconductor.

(D) Ferromagnetic substances are those that are strongly attracted by a magnetic field and show permanent magnetism even when the magnetic field is removed.
Examples include $Fe$,$Co$,$Ni$,$CrO_2$,and $Fe_3O_4$.
Analyzing the given options:
- $NaCl$ is diamagnetic.
- $H_2O$ is diamagnetic.
- $O_2$ is paramagnetic.
- $CrO_2$ is ferromagnetic.
Therefore,the correct option is $D$.

(B) $Fe$,$Co$,and $Ni$ are ferromagnetic substances.
$Zn$ is diamagnetic in nature.