Type of solid and Their properties Questions in English

(C) Amorphous solids do not have an ordered arrangement of particles (i.e.,no long-range order) and do not possess a sharp melting point like crystalline solids.
When heated,they gradually soften and become pliable,exhibiting properties similar to liquids.
Therefore,they are often referred to as supercooled liquids.

(C) $Silicon$ $(Si)$ has a diamond-like crystal structure where each $Si$ atom is covalently bonded to four other $Si$ atoms in a tetrahedral arrangement. This continuous three-dimensional covalent bonding results in a giant covalent structure,which is classified as a $Network \ solid$.

(D) The correct answer is $D$.
Metals typically have low lattice energy compared to ionic compounds because metallic bonding is non-directional and involves delocalized electrons.
Option $A$ describes the electron sea model of metallic bonding,which is correct.
Option $B$ is correct as metals often crystallize in structures like $fcc$ or $hcp$ with high coordination numbers (e.g.,$12$).
Option $C$ is correct as metals pack efficiently to maximize stability.

(D) The process described is known as $quenching$. Heating steel to bright redness and then cooling it suddenly by plunging it into oil or water increases the hardness of the steel but also makes it brittle. Therefore,the steel becomes $Hard$ and $brittle$.

(D) When a steel object like a clock spring is heated to redness and then suddenly cooled by plunging it into cold water,a process known as $quenching$ occurs. This rapid cooling prevents the formation of a soft,equilibrium microstructure and instead results in the formation of $martensite$,which makes the metal $hard$ and $brittle$.

(C) Solids can be classified into two types: crystalline and amorphous.
Amorphous solids do not have a regular,repeating arrangement of particles,meaning they are not always crystalline.
Therefore,the statement that solids are always in crystalline form is incorrect.

(B) Molecular solids consist of molecules held together by weak van der Waals forces or hydrogen bonds.
Due to these weak intermolecular forces,they generally have low melting points and are often volatile.
They are soft and poor conductors of electricity.

(C) Amorphous solids do not have a long-range order of particles and do not possess a sharp melting point. When they are heated and then cooled rapidly,they exhibit properties similar to liquids,which is why they are often referred to as $supercooled \ liquids$.

(A) primitive unit cell is one in which the constituent particles are present only at the corner positions of the unit cell.
Among the given options,the $Simple \ cubic$ unit cell is a primitive unit cell because particles are located only at the corners.
$Body-centered$ and $Face-centered$ unit cells are types of centered unit cells.

(D) Amorphous solids are those in which the constituent particles do not have a long-range ordered arrangement. $Glass$ and $Tar$ are classic examples of amorphous solids (also known as supercooled liquids). $KCl$ is a crystalline solid with a regular lattice structure. Therefore,both $Glass$ and $Tar$ are amorphous.

(C) Ionic solids consist of ions held together by strong electrostatic forces of attraction.
These forces result in high melting points and hardness.
In the solid state,ions are fixed in their lattice positions,making them electrical insulators.
However,in the molten state or in aqueous solution,the ions become free to move,allowing them to conduct electricity.

(C) Crystalline solids are anisotropic in nature,meaning their physical properties (like refractive index or electrical conductivity) vary with the direction of measurement. Amorphous solids,on the other hand,are isotropic. Therefore,being isotropic is a characteristic of amorphous solids,not crystalline solids.

(C) The $7$ crystal systems are classified based on their unit cell parameters ($a, b, c$ and $\alpha, \beta, \gamma$).
In the $Triclinic$ system,$a \neq b \neq c$ and $\alpha \neq \beta \neq \gamma \neq 90^{\circ}$.
This system possesses the lowest symmetry and is considered the most asymmetric crystal system.

(B) Ionic solids consist of ions held together by strong electrostatic forces of attraction,which require a large amount of energy to overcome. Therefore,they generally possess the highest melting points compared to molecular,covalent (network),or amorphous solids.

(D) Cleavage is the property of a crystal to break along specific planes of weakness. This occurs because the constituent particles (atoms,molecules,or ions) are arranged in specific planes,and the forces of attraction between these planes are relatively weaker than the forces within the planes. Therefore,when stress is applied,the crystal breaks along these planes.

(A) Crystalline solids are characterized by a regular and repeating arrangement of their constituent particles (atoms,ions,or molecules) that extends over a long distance in the crystal lattice. This is known as long-range order. In contrast,amorphous solids exhibit only short-range order.

(C) Wax is a non-polar molecular solid.
In molecular crystals,the constituent particles are molecules held together by weak van der Waals forces.
Since wax consists of long-chain hydrocarbons held by these weak forces,it is classified as a molecular crystal.

(D) Crystalline solids have a regular,repeating arrangement of particles over long distances. Common salt $(NaCl)$,sugar $(C_{12}H_{22}O_{11})$,and iron $(Fe)$ are examples of crystalline solids. Rubber is an amorphous solid,which lacks a long-range ordered structure.

(B) In solid $NaCl$,the ions ($Na^+$ and $Cl^-$) are held together by strong electrostatic forces of attraction in a rigid crystal lattice.
Because these ions are fixed in their positions and are not free to move,they cannot conduct electricity in the solid state.
However,in the molten state or in an aqueous solution,the ions become free to move,allowing the substance to conduct electricity.

(D) Amorphous solids are those in which the constituent particles do not have a long-range ordered arrangement.
$CsCl$,$NaCl$,and $CaF_2$ are crystalline solids because they possess a regular,repeating three-dimensional arrangement of particles.
Glass is an example of an amorphous solid,often referred to as a supercooled liquid.

(D) The statements provided describe the properties of amorphous solids,not crystalline solids.
$(1)$ Crystalline solids have a sharp melting point,whereas amorphous solids do not. Thus,statement $(1)$ is $False$ $(F)$.
$(2)$ Amorphous solids gradually soften upon heating,while crystalline solids melt sharply. Thus,statement $(2)$ is $False$ $(F)$.
$(3)$ Crystalline solids have a regular,long-range order,whereas amorphous solids have an irregular arrangement. Thus,statement $(3)$ is $False$ $(F)$.
$(4)$ Crystalline solids show a sharp change in volume upon melting,not a gradual one. Thus,statement $(4)$ is $False$ $(F)$.
Therefore,the correct sequence is $FFFF$.

(C) In crystalline $NaCl$,the ions present are held in a rigid lattice structure and are not free to move,which is necessary for the conduction of electricity.

(A) Due to the high content of silica $(SiO_2)$,dicalcium silicate $(C_2S)$ sets at the slowest rate among the components of cement.

(B) In ionic solids,the ions are held in fixed positions within the crystal lattice by strong electrostatic forces of attraction. Because they are not free to move,they cannot conduct electricity in the solid state.

(C) Isomorphous substances are those that have the same crystalline structure and similar chemical composition.
$ZnSO_4 \cdot 7H_2O$ (Zinc sulfate heptahydrate) and $MgSO_4 \cdot 7H_2O$ (Magnesium sulfate heptahydrate) are isomorphous because they both crystallize in the orthorhombic system and have the same number of atoms bonded in a similar fashion.
Therefore,the correct pair is $ZnSO_4$ and $MgSO_4$.

(B) The phenomenon where certain polar crystals produce an electric current when heated is known as the $Pyroelectric \ effect$.
Note: While $Piezoelectric \ effect$ refers to the production of electricity due to mechanical stress,$Pyroelectric \ effect$ specifically refers to the response to temperature changes.

(D) In molecular crystals like wax,the constituent particles are molecules held together by weak intermolecular forces such as van der Waals forces or hydrogen bonding.
These forces are relatively weak compared to the strong covalent bonds within each molecule.
Therefore,molecular crystals tend to have lower melting points compared to covalent or metallic crystals,where the bonding is stronger.

(D) Molecular crystals are held together by weak van der Waals forces,making them soft and resulting in a low melting point.

(A) The packing fraction of a lattice structure is defined as the fraction of the total volume occupied by the atoms in a unit cell.
For a primitive cubic unit cell,the number of atoms per unit cell $(z)$ is $1$ and the edge length $(a)$ is $2r$.
Packing fraction $= \frac{z \times \frac{4}{3} \pi r^{3}}{a^{3}} = \frac{1 \times \frac{4}{3} \pi r^{3}}{(2r)^{3}} = \frac{\pi}{6} \approx 0.52$.
Statement $A$ is incorrect because a diamond unit cell contains $8$ carbon atoms,not $4$. However,in the original options provided,statement $C$ stated $0.48$,which is also incorrect. Given the standard chemistry context,the number of atoms in a diamond unit cell is $8$ (making $A$ incorrect),and the packing fraction of a primitive cell is $0.52$ (making the original $C$ incorrect). Assuming the question asks for the incorrect statement,$A$ is the most fundamentally incorrect statement regarding the diamond structure.

(B) $p-$type semiconductors are obtained by doping group $14$ elements like silicon or germanium with group $13$ elements (electron-deficient impurities) such as $B, Al, Ga,$ or $In$.
Since boron belongs to group $13$,doping silicon with boron creates electron holes,resulting in a $p-$type semiconductor.

(B) In the solid state,$I_2$ (Iodine),$S_8$ (Sulphur),and $P_4$ (Phosphorus) exist as molecular solids held together by weak van der Waals forces.
Silicon $(Si)$ forms a giant network structure where atoms are linked by covalent bonds,thus existing as a covalent (network) crystal.

(D) Among the given metallic oxides,$CrO_2$ is strongly attracted by a magnetic field.
This magnetic property persists even after the removal of the external magnetic field.
Therefore,$CrO_2$ is classified as a metallic and ferromagnetic compound.

(D) $p-$type semiconductor is formed when a semiconductor is doped with an impurity that has fewer valence electrons than the host material,creating an electron deficiency or 'hole'.
$Ge$ doped with $P$ ($Group$ $15$) creates an $n-$type semiconductor due to extra electrons.
$Si$ doped with $S$ ($Group$ $16$) creates an $n-$type semiconductor.
$NaCl$ yellow crystals are due to $F-$centers (anionic vacancies),not semiconductor behavior.
$Cu_{1.98}O$ is a metal-deficient oxide. Here,some $Cu^+$ ions are replaced by $Cu^{2+}$ ions to maintain electrical neutrality,creating 'holes' in the lattice. This makes it a $p-$type semiconductor.

(B) Refractory materials are substances that retain their strength at high temperatures.
Key properties of refractory materials include:
$1$. High melting point.
$2$. Chemical inertness (resistance to corrosion).
$3$. Low thermal conductivity (to act as insulators).
$4$. Low electrical conductivity.
Therefore,high thermal conductivity is not a typical property of a refractory material,as they are generally used for insulation.

(C) Solid $NaCl$ is a bad conductor of electricity because in the solid state,the $Na^+$ and $Cl^-$ ions are held together by strong electrostatic forces in a rigid crystal lattice.
Due to this,there is no mobility of ions,which is required for the conduction of electricity.
In the molten state or aqueous solution,these ions become free to move and thus conduct electricity.
Therefore,the correct option is $C$.

(C) Molecular solids are composed of molecules held together by weak van der Waals forces or dipole-dipole interactions.
$SiC$ (Silicon carbide) is a covalent network solid.
Graphite is a covalent network solid.
Diamond is a covalent network solid.
Fullerene $(C_{60})$ consists of discrete molecules held together by van der Waals forces,making it a molecular solid.

(B) Crystalline solids possess a long-range order,meaning the constituent particles (atoms,molecules,or ions) are arranged in a regular,repeating pattern throughout the entire crystal lattice.
Because of this uniform and periodic arrangement,all constituent particles experience identical environments and bonding forces.
Consequently,all bonds in the crystal break at the same specific temperature,resulting in a sharp melting point.
Therefore,option $B$ is the correct answer.

(D) Antiferromagnetic substances are characterized by a domain structure where the magnetic moments of the domains are aligned in a compensatory manner,such that the net magnetic moment is zero. This occurs when the spins are aligned in equal numbers in opposite directions,as shown in option $D$.

(C) Materials that produce an electric current when they are subjected to mechanical stress are called piezoelectric materials. $Quartz$ is a well-known example of a piezoelectric material and is extensively used in various electronic devices.

(C) The melting point of a solid depends on the strength of the intermolecular forces holding the particles together.
$(c)$ Molecular solids are held together by weak van der Waals forces or dipole-dipole interactions,which require very little energy to overcome.
In contrast,ionic,metallic,and covalent network solids are held together by strong electrostatic,metallic,or covalent bonds,respectively,resulting in high melting points.

(D) The melting point of a solid depends on the nature of the forces holding its particles together.
$1$. $Ice$ $(H_2O)$ is a molecular solid held by hydrogen bonds,which is relatively weak.
$2$. $Dry \, ice$ $(CO_2)$ is a molecular solid held by weak van der Waals forces.
$3$. $NaCl$ is an ionic solid with strong electrostatic forces of attraction,having a melting point of approximately $1074 \ K$.
$4$. $SiO_2$ (Quartz) is a covalent network solid where silicon and oxygen atoms are linked by strong covalent bonds in a three-dimensional structure. This network requires a very high temperature to break,resulting in a melting point of approximately $1986 \ K$.
Therefore,$SiO_2$ has the highest melting point among the given options.

(B) Molecular solids are composed of molecules held together by van der Waals forces.
$C_{60}$ (Buckminsterfullerene) consists of discrete $C_{60}$ molecules held together by weak van der Waals forces,making it a molecular solid.
Graphite is a covalent network solid.
Gold is a metallic solid.
$Ca_3(PO_4)_2$ is an ionic solid.

(B) Carborundum is the common name for silicon carbide $(SiC)$.
It consists of a three-dimensional network of silicon and carbon atoms linked by strong covalent bonds.
Therefore,it is classified as a covalent or network solid.

(C) The element $Po$ (Polonium) is the only element in the oxygen family that crystallizes in a simple cubic lattice structure in its solid state.

(B) Gypsum $(CaSO_4 \cdot 2H_2O)$ is added to cement clinker during the grinding process. It acts as a retarder,which slows down the hydration process of tricalcium aluminate $(C_3A)$,thereby increasing the initial setting time of cement.

(C) In an ionic solid,the ions are held together by strong electrostatic forces of attraction in a rigid crystal lattice.
Because the ions are in fixed positions,they are not free to move.
Since electrical conductivity requires the movement of charged particles,ionic solids are poor conductors of electricity in the solid state.

(C) The process of heating steel to a high temperature and then cooling it slowly is known as $Annealing$.
This process makes the steel softer and more ductile by relieving internal stresses.

(B) Isomorphous substances have the same crystal structure and similar chemical composition.
$NaF$ and $MgO$ are isomorphous as they have the same crystal lattice structure.
$CaCl_2$ and $K_2S$ are isomorphous.
$MgCO_3$ and $KNO_3$ are isomorphous.
$CuSO_4 \cdot 5H_2O$ and $FeSO_4 \cdot 7H_2O$ are not isomorphous because they have a different number of water molecules of crystallization,which leads to different crystal structures.