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Voids are the empty spaces present between atoms or ions, when they are packed within the crystal.

Correct answer is: (A) 2

Number of atoms per unit cell in fcc = 4

Number of atoms per unit cell in bcc = 2

\(\therefore\) Difference = 4 - 2 = 2

∆T_b /∆T_f = Kb/Kf = 0.178 x 1.86 / 0.52 = 0.6367 K

T_f = -0.6367 K 

Correct answer is: (A) long range order

(ii) Low temperature

• Unit cell : It is the smallest repeating structural unit of a crystalline solid (or crystal lattice) which when repeated in different directions produces the crystalline solid (lattice). 
• The crystal is considered to consist of an infinite number of unit cells.
• The unit cell possesses all the characteristics of the crystalline solid.

• Since the energy difference between valence band and conduction band in semiconductor is not large, the electrons from valence band can be promoted to conduction by heating. 
• Hence electrical conductivity of a semiconductor increases with temperature.

(b) Si doped with As

Si doped with As is n-type semiconductor.

(b) amorphous solids

Molecular solids are amorphous solids.

The arrangement of particles in this solid is regular.

Correct answer is: (A) amorphous

Depending on orderly arrangement of the constituent particles, the solids are classified into two types :

Crystalline solids. For example, diamond, NaCl, K₂SO_4, etc. Amorphous solids or non-crystalline solids. 

For example, 

tar, glass, plastics, rubber, butter, etc.

Correct answer is: (A) one half

• The solid state of matter is characterised by strong interparticle forces of attraction.
• There is regularity and periodicity in the arrangement of constituent particles of solid.
• Generally solids are hard, incompressible and rigid except some solids like Na, K, P which are soft.
• The constituent particles of solids like molecules, atoms or ions have fixed stationary positions in solid and can only oscillate about their equilibrium or mean positions. Hence, they have fixed shape and cannot be poured like liquids.
• Crystalline solids have sharp melting points and they melt at a definite temperature. Amorphous solids do not have sharp melting points.
• They are anisotropic or isotropic. 

The smallest constituent particles of various solids are atoms, ions or molecules. All such small constituents are referred to as 'particles'

Correct answer is: (C) Copper

i. Matter can exist in three states namely, solid, liquid and gas. Under a given set of conditions of temperature and pressure, the most stable state of a substance depends upon the net effect of two opposing forces: intermolecular forces and thermal energy.

ii. Intermolecular forces tend to keep the constituent particles (atoms, ions or molecules) closer, whereas thermal energy tends to keep them apart by making them move faster. 

iii. The competition between molecular interaction energy due to intermolecular forces and thermal energy determines whether a given substance under a given set of condition is a gas, a liquid or a solid.

iv. At sufficiently low temperature, the thermal energy is low and molecular forces are very strong. As a result, the intermolecular forces keep the constituents so close that they cling to one another and occupy fixed positions and the substance exists in solid state.

Correct answer is: (D) all of these

These are crystalline solids formed by atoms of the same metallic element held together by metallic bonds.

The intermolecular forces involved in molecular crystals are as follows :

(1) Weak dipole-dipole interactions : The solids constituting polar molecules like HCl, H₂O, SO₂, etc. which possess permanent dipole moment involve weak dipole-dipole interactions.

(2) Very weak dispersion or London forces : The solids consisting of nonpolar molecules like CH₄,H₂, etc. involve weak dispersion forces. They are also involved in monoatomic solids like Ar, Ne.

(3) Intermolecular Hydrogen bonds :

• In this crystalline solids, the constituent particles are the molecules which contain hydrogen atom linked to highly electronegative atom like F,O or N.
• In these, molecules are held by hydrogen bonds in which H atom of one molecule is bonded to electronegative atom (like F, N or O) of another molecule.
• Since hydrogen bonding is weak, these solids have very low melting points and generally at room temperature they exist in the liquid or gaseous state.
•  They are non-conductors of electricity.

A solid is defined as that form of matter which possesses rigidity and hence possesses a definite shape and a definite volume.

Solid is one of the three main states of matter, along with liquid and gas. The matter is the "stuff" of the universe, the atoms, molecules, and ions that make up all physical substances. In a solid, these particles are packed closely together and are not free to move about within the substance.

I hope my answer is correct

1. Metallic crystals are solids formed by atoms of the same metallic element held together by metallic bonds. 

2. Metallic crystals have high melting point and boiling point. 

3. Metals are malleable and can be hammered into thin sheets. 

4. Metals are ductile and can be drawn into thin wires. 

5. Metals are good conductors of heat and electricity. 

6. Examples are Cu, Ag, Au, Ni, etc.

The characteristics of molecular crystals are as follows :

1. The constituent particles of these solids are molecules (or unbonded single atoms) of the same substance.

2. The atoms within the molecules are bonded by covalent bonds.

3. The molecules are held together by intermolecular forces of attraction.

Characteristics of Solid State :

• Solids have definite mass, volume and shape. 
• Intermolecular forces are strong. 
• The constituent particles (atoms, molecules or ions) have fixed positions and can only oscillate about their mean positions. 
• They are incompressible and rigid.

The solid state is characterized by the following properties:

i. Solids have definite mass, volume, shape and density. Usually, the density of solid state is greater than the density of liquid and gaseous state. Water and mercury are exceptions. The density of ice (solid state of water) is lower than the density of liquid state of water. The density of mercury (which exists in liquid state) is very high (13.6 g mL^-1 ).

ii. Solids are usually hard, incompressible and rigid. Some solids like sodium, potassium and phosphorous are exceptions; they are soft. Solids cannot be compressed because the intermolecular distance of separation between neighbouring molecules is very small.

iii. In a solid state, intermolecular forces of attraction between the constituent particles are stronger than those present in liquid and gaseous states.

iv. All pure solids have characteristic melting points which depend on the extent of intermolecular forces present in the solid state. Stronger the intermolecular forces of attraction, higher is the melting point of the solid. Weaker the intermolecular forces of attraction, the lower is its melting point. Hence, depending on the intermolecular forces of attraction, melting points of the different solids range from almost absolute zero (helium) to a few thousand Kelvin (diamond).

v. The intermolecular forces of attraction hold the constituent particles of the solids tightly. Hence the particles cannot change their positions and remain stationary at one position. Therefore, solids cannot flow like liquids.

1. Definite mass, volume, and shape.
2. Short Intermolecular distance.
3. Strong Intermolecular Forces.
4. The constituent particles remain fixed at their positions and can only oscillate about their mean positions.
5. Solids are incompressible and rigid.
6. High Density.

Arrangement in image A indicates the substance is crystalline. 

Arrangement in image B indicates the substance is amorphous.

Density = Mass of unit cell/Volume of unit cell 

8.93 = (4 x 63.5)/(a³ x 6.02 x 10²³). 

a³ = 47.24 x 10^-24 

a = 3.6 x 10^-8 cm. = 360 pm. 

Correct answer is

(a) 3.011 × 10²³, 6.022 × 10²³

1. P₄ – Molecular solid 

2. Brass – Metallic solid 

3. Diamond – 

4. NaCl – Ionic solid 

5. Iodine – Molecular solid

The characteristics of covalent network crystals are as follows :

• The constituent particles in these solids are atoms. 
• The atoms in these crystals are held by covalent bonds forming a rigid three dimensional network which gives a giant molecule. Hence, the entire crystal is a single molecule.
• These crystals are very hard (or hardest) and most incompressible.
• They have high melting points and boiling points.
• Since the electrons are localised they are poor conductors of heat and electricity.
• Example : Quartz (SiO₂), diamond. 

The correct option is (b) No definite geometry.

No definite geometry is not a characteristic of a covalent compound. The covalent compound has definite geometry because of the bond forms.

The correct option is (b) 2.

In ccp, number of atoms present per unit cell = 4

Since in cubic closed packing, the number of tetrahedral voids is equal to twice the number of atoms present per unit cell, hence

Number of tetrahedral voids = 2 × 4 = 8

These ∗ voids are uniformly distributed over each of the 4 body diagonals. Therefore,

Number of tetrahedral voids present on each body diagonal in CCP unit cell = 8/4 = 2

It has a tendency to flow like liquid.

2N of tetrahedral voids generated if the number of close packed sphere be N in a crystal.

Correct answer is: (D) 180 pm

2r⁺ + 2r^– = 520

\(\therefore\) \(r^++r^-=\cfrac{520}{2}\)=r^-=260 – 80 = 180 pm.

Correct answer is: (B) increases

Correct answer is: (C) 1Cs⁺ and 1Cl^–

Correct answer is: (C) ABABA....

Rank is the number of atoms per unit cell of a crystal. 

In f c c Contribution of atoms present at the corners = 8 x 1/8 -1

Contribution of atoms present at faces  = 6 x 1/2-3

∴ Rank = 1 + 3 = 4.

6 and 4 respectively

(a) in fcc structure : 12

(b) in bcc structure : 8

The process of introducing atoms of other elements as impurity into an insulator to make it semiconductor is called doping. Doping of silicon or germanium with electron rich impurities like P, As, Sb results in formation of n-type semiconductors whereas ptype semiconductors are formed by adding elements of group 13 like B, Al,Ga.

Correct answer: (A) Solids are always crystalline in nature.

(a) 14

(b) 9

(8) 8

In the given hcp lattice, Y atoms are present at 12 corners and 2 face centres.

\(\therefore\) Number of Y atoms \(= \frac{1}{2} \times 12 + 2 \times \frac{1}{2} = 3\)

There are 6 tetrahedral voids, the number of X atoms \(=\frac{1}{3} \times 6 = 2\)

\(\therefore\) Formula of the compound is X₂Y₃.

The conductivity of semiconductor is too low, which can be increased by adding an appropriate amount of suitable impurity. This process is called doping.

Doping can be done with an impurity which is electron rich or electron deficient as compared to the intrinsic semiconductor silicon or germanium.

Such impurities introduce electronic defects in them. Electronic defects correspond to defects in ionic crystals due to the electrons.

The correct option is C) the doped silicon piece will become p-type.

p type of semiconductor is obtained when Silicon is doped with a trivalent impurity like Aluminium. Aluminium is a p-type dopant, which means that when a semiconductor i.e. silicon is doped with aluminium, it creates a hole (positively charged carrier) by accepting an electron from the silicon atom. Electrical conductivity of semiconductors increases and resistivity remains the same.

Total number of electrons in doped silicon will be more than in original silicon.