### Classification of crystalline solids - class-XII

 Description: classification of crystalline solids Number of Questions: 74 Created by: Palash Sundaram Tags: the solid state chemistry solid state
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Which of the following statement is not correct about molecular crystals?

1. They are generally soft and easily compressible.

2. They are good conductors of electricity as the electrons are delocalised in the bonds.

3. They have low melting and boiling points.

4. They consist of polar or non-polar molecules.

Correct Option: B
Explanation:

In molecular crystals, atoms are bounded by weak van der Walls forces. They have no free electrons in them. So, they are electrical insulators.

Hence, the correct answer is option B.

Examples of few solids are given below. Find out the example which is not correctly matched.

1. Ionic solids - $NaCl$, $ZnS$

2. Covalent solids - $H _2,I _2$

3. Molecular solids - $H _2O _{(s)}$

4. Metallic solids - $Cu$, $Sn$

Correct Option: B
Explanation:

In ${ H } _{ 2 }\quad and\quad { I } _{ 2 }$, molecules are attracted by weak van der Waals attractions. So, they are molecular solids.

Hence, option B is not a correct match.

Which of the solids show the following properties?
(i) Electrical conductivity
(ii) Malleability
(iii) Ductility
(iv) Fairly high melting point

1. Ionic solids

2. Covalent solids

3. Metallic solids

4. Molecular solids

Correct Option: C
Explanation:

In the given options, both ionic and metallic solids are electrical conductors and have high melting point. But only metallic solids are malleable and ductile.

So, the correct answer is option C.

Ionic solids conduct electricity in molten state but not in solid state because:

1. in molten state free ions are loosely bound which are not free to move in the solid state

2. in solid state ionic solids are hard, brittle and become soft in molten state

3. all solids conduct electricity in molten state

4. in solid state ions are converted to atoms which are insulators.

Correct Option: A
Explanation:

In solid state, atoms in ionic solids are bonded by strong ionic bonds. They are able to move freely. So, they do not conduct electricity in solid state. While in molten form, the ions and electrons are free to move. So, they conduct electricity in molten state.

So, the correct answer is option A.

Which of the following forms a molecular solid when solidified?

1. Calcium fluoride

2. Silicon dioxide

3. Carbon dioxide

4. Sodium chloride

Correct Option: C
Explanation:

In the given options, Calcium Fluoride and Sodium Chloride are the ionic crystals due to presence of ionic bond in them.

Silicon dioxide is network solid due to strong intermolecular covalent bond.
In carbon dioxide, the molecules are bonded by weak van der Walls force. Hence, they are molecular solids.
So, the correct answer is option C.

Solid $X$ is a very hard solid which is electrical insulator in solid as well as in molten state and has extremely high melting point. What type of solid is it?

1. Ionic solid

2. Covalent solid

3. Metallic solid

4. Molecular solid

Correct Option: B
Explanation:

Covalent solids have high melting point due to their interconnected covalent bonds. Since there are no free electrons present in covalent solids, so they do not conduct electricity in solid state as well as molten state. Some of the examples are Diamond and Quartz.

So, correct answer is option B.

Graphite cannot be classified as:

1. conducting solid

2. network solid

3. covalent solid

4. ionic solid

Correct Option: D
Explanation:

Since graphite is an allotrope of carbon hence, each atom is linked to each other through a covalent bond. Therefore, graphite is a covalent solid.

Hence, it cannot be classified as an ionic bond.

Hence, the correct answer is option $\text{D}$.

Which of the following is not the characteristic of ionic solids?

1. Very low value of electrical conductivity in the molten state

2. Brittle nature

3. Very strong forces of interactions

4. Anisotropic nature

Correct Option: A
Explanation:

In molten state, the ionic solids have free ions in them. Ions help in the conduction of electricity. Due to these free ions the electrical conductivity of ionic compounds in molten state is very high.

So, option A is not correct regarding the characteristics of ionic compounds.
So, option A is correct answer.

Which of the following is network solid?

1. $SO _{2(solid)}$

2. $I _2$

3. Diamond

4. $H _2O _{(ice)}$

Correct Option: C
Explanation:

A network solid or covalent network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule.

In diamond, the carbon atoms are held together by strong covalent bonds. It is a giant molecule. Thus, it is a network solid.
So, option $C$ is correct.

Which of the following is not true about the ionic solids?

1. Bigger ions form the close packed structure.

2. Smaller ions occupy either the tetrahedral or the octahedral voids depending upon their size.

3. Occupation of all the voids is not necessary.

4. The fraction of octahedral or tetrahedral voids occupied depends upon the radii of the ions occupying the voids.

Correct Option: D
Explanation:

In ionic solids anions (which are normally longer in size than cations forms closed pack array.

The cation occupies one of the two types of holes remaining between the anions (either tetrahedral void or octahedral void).
Depending on the relative sizes of cations and anions, the voids are filled. Occupation of voids depends on the stoichiometry of the compounds. It is not necessary that all voids get filled.

What makes the molecular crystals solid at low temperature?

1. Sharing of electrons.

2. Transfer of electrons.

3. Vander Waal's force arising out of polarisation.

4. All of the above.

Correct Option: C
Explanation:

Vander Waal's forces make the molecular crystals, solids at low temperature.

Its properties are dictated by the weak nature of these intermolecular forces.

A molecular crystalline solid:

1. is very hard

2. is volatile

3. has a high melting point

4. is a good conductor

Correct Option: B
Explanation:

Molecular solid is a solid in which the constituent particles are atoms or molecules which are held together by weak intermolecular forces i.e. van der Waals forces. Due to weak forces, they are volatile.

Wax is an example of:

1. ionic crystal

2. covalent crystal

3. molecular crystal

4. metallic crystal

Correct Option: C

$KCl(s)$ is:

1. An ionic substance

2. A polar covalent substance

3. A nonpolar covalent substance

4. An amorphous substance

5. A metallic network

Correct Option: A
Explanation:

Potassium chloride KCl is a metal halide salt composed of potassium and chloride. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water and its solutions have a salt-like taste.

In aqueous solution,

$KCl\longrightarrow { K }^{ + }+{ Cl }^{ - }$

It is an ionic substance in solid state.

This allows many solids to conduct electricity :

1. Hydrogen bonding

2. Ionic bonding

3. Metallic bonding

4. Nonpolar covalent bonding

5. Polar covalent bonding

Correct Option: C
Explanation:

Metallic bonding is the strong attraction between closely packed positive metal ions and a sea of delocalised electrons. The delocalised electrons are able to move through the metallic structure. When a potential difference  is applied, they will move together, allowing an electric current to flow through the metal.

The nature of bonds in compounds of C and Si is:

1. ELectrovalent

2. Covalent

3. Metallic

4. Covalent and electrovalent

Correct Option: B
Explanation:

Carbon and silicon are chemical elements with atomic number 6 and 14. they are nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. Option-B.

$I$. Metallic solids tend to be very brittle.

$II$. Metallic bonds are broken quite easily.

1. Statement $I$ is true, Statement $II$ is true

2. Statement $I$ is true, Statement $II$ is false

3. Statement $I$ is false Statement $II$ is true

4. Statement $I$ is false, Statement $II$ is false

Correct Option: D
Explanation:

Metallic solids are generally non-brittle or highly malleable and ductile. Also metallic bond is one of the strongest bonds.

Therefore both statements are false.

Which of the following statements is true?

1. Molecular crystals are very hard and incompressible

2. Ionic crystals have very low volatility

3. Metallic bond is directional and rigid

4. Boron nitride has an ionic crystal structure

Correct Option: B
Explanation:

Ionic crystals have very low volatility. Generally, ionic solids are having ionic bonds between the constituent atoms.

Ionic bonds are very strong bonds. So they are less volatile.

Iodine crystals are

1. Metallic solid

2. Ionic solid

3. Molecular solid

4. Covalent solid

Correct Option: C

Which of the following solid is made up of ions?

1. Sugar

2. Common salt

3. Polythene

4. Wood

Correct Option: B

Which of the following ionic solids has the lowest melting point?

1. $KCl$

2. $NaCl$

3. $LiF$

4. $LiCl$

Correct Option: A
Explanation:

Melting point of an ionic compound is determined by the electrostatic attraction between cations and anions. It takes a lot of energy to overcome this attraction to allow the ions to move freely and form a liquid. The factor witch effect melting point is charge of the ion. Since, $KCl$ has $+1$ and $-1$ charge on its' cations and anions respectively. Hence, it has the lowest melting point.

Hence, the correct option is $A$

Statement: An ionic solid has some point defect but its experiment density is equal to its theoretical density.

State whether the given statement is true or false.

1. True

2. False

Correct Option: A
Explanation:

An ionic solid has some point defect but its experimental density is equal to its theoretical density. The type of defect is Frenkel effect.

When an ion leaves its correct lattice site and occupies an interstitial site, Frenkel defect is observed. Hence, the density of the crystal is not affected.

In a Schottky defect, the density of the crystal decreases.

Hence, the given statement is $\text{true}$

AB is an ionic solid. The ionic radii of A+ and B- are respectively Rc and Ra. Lattice energy of AB is proportional to

1. Rc/Ra

2. Rc + Ra

3. Ra/Rc

4. 1/(Rc+Ra)

Correct Option: D

Crystals which are good conductor of electricity  and heat are known as:

1. Ionic crystals

2. Convalent crystals

3. Molecular crystals

4. All the above

Correct Option: A

Carborundum is a :-

1. molecular solid

2. covalent solid

3. ionic solid

4. amorphous solid

Correct Option: B

Graphite is a lubricating solids due to

1. Network structure

2. Free valence electeons

3. London forces between layers

4. Both $(1)$ and $(3)$

Correct Option: A

The polar molecular soild is:

1. Naphthlene

2. Dry ice

3. Sulphur dioxide

4. Iodine

Correct Option: A

Graphite is a :

1. metallic crystal

2. covalent crystal

3. ionic crystal

4. molecular crystal

Correct Option: B

The lattice of a covalent crystal is composed of :

1. atoms

2. molecules

3. ions

4. compounds

Correct Option: A
Explanation:

A covalent network crystal consists of atoms at the lattice points of the crystal, with each atom being covalently bonded to its nearest neighbour atoms.

The covalently bonded network is three-dimensional and contains a very large number of atoms.

Examples of these crystals include graphite and diamond.
In these crystals, the atoms form covalent bonds with one another.

The thermal conductivity of silver and copper is high because they have following binding :

1. Metallic

2. Ionic

3. Covalent

4. Vander Waal

Correct Option: A
Explanation:

The thermal conductivity of silver and copper is high because they have metallic bonding.

Silver and copper are metals. They form metallic bonds. They contain mobile electrons immersed in a sea of positively charged metal cations.

These mobile electrons can move from one end of metal to other end. Hence, they conduct electricity.

Therefore, option A is correct.

The molecular range for materials is :

1. $10^{-12}m$

2. $10^{-10}m$

3. $10^{-11}m$

4. $10^{-9}m$

Correct Option: D
Explanation:

The molecular range for materials is $10^{-9}m$. It can also be expressed in terms of nanometers. $1 nm =10^{-9}m$.

Metallic bonding is explained by :

1. band model

2. electron-sea model

3. both (a) and (b)

4. None of these

Correct Option: C
Explanation:

Both theories have their own arguments to explain metallic bonding.
Each metal atom allows its electrons to roam freely, so these atoms become positively charged cations. These cations are kind of like a positively charged island and are surrounded by a sea of negatively charged electrons.

Some of the following properties are important in determining whether an element has metallic properties.
I : atomic number
II : atomic weight
III: number of valence electrons
IV: number of vacant atomic orbitals
V: total number of electronic shells in the atom
Select correct properties from the codes given below:

1. I, II, III, IV

2. I, III, IV, V

3. III, IV

4. III, IV, V

Correct Option: C
Explanation:

The following properties are important in determining whether an element has metallic properties.
III: number of valence electrons
IV: number of vacant atomic orbitals
All metals are electropositve elements and have a tendency to lose electrons.  Alkali metals and alkaline earth metals contain one and two valence electrons respectively.They readily lose these electrons and show metallic properties. Transition metals have a number of vacant d orbitals and show variable valency. Due to the presence of vacant d orbitals, they show variable valence.

A solid melt slightly above $273K$ and is a poor conductivity of heat and electricity. To which of the following categories does it belong?

1. Ionic solid

2. Covalent solid

3. Metallic solid

4. Molecular solid

Correct Option: D

Which of the following is an example of molecular solid?

1. Zinc Sulphide

2. Magnesium Oxide

3. Dry ice

4. Diamond

Correct Option: C
Explanation:

Molecular solids refer to those solids which are composed of molecules held together by the van der Waals forces.

Examples are hydrogen, carbon dioxide etc.

ZnS is a crystalline solid.
MgO is an ionic solid.
Diamond has a network structure.

Hence, dry ice $(CO _2)$ is an example of a molecular solid.

A solid melts slightly above $273$ K and is a poor conductor of heat and electricity. To which of the following categories does it belong?

1. Ionic

2. Covalent

3. Metallic

4. Molecular

Correct Option: D
Explanation:

Metals are good conductors of heat and electricity with variable melting points.
Ionic solids are also good conductors of heat and electricity with very high melting points.
Covalent solids are non conductor of electricity and heat with very high melting points due to their strong bonding.
Molecular solids are poor conductors of heat and electricity and they have lower melting point than ionic solids.

Molecular crystals exists in:

1. crystalline state

2. amorphous state

3. non-crystalline state

4. None of the above

Correct Option: A,B,C
Explanation:

Molecular crystals exist in all crystalline state, an amorphous state, and non-crystalline state. Molecular crystals are substances that have relatively weak intermolecular binding, such as dry ice (solidified carbon dioxide), solid forms of the rare gases (e.g., argon, krypton, and xenon).

What state are most ionic compounds at room temperature?

1. Solid

2. Liquid

3. Gas

4. Plasma

Correct Option: A
Explanation:

Generally, ionic compounds exist in solid state due to strong electrostatic ionic forces present between the molecules of solids.

For example;  NaCl or KCl

Hence, option $A$ is correct.

Metallic solids are always opaque because:

1. they reflect all the incident light

2. they scatter all the incident light

3. the incident light is readily absorbed by the free electrons in a metal

4. the energy band traps the incident

Correct Option: C
Explanation:

Metals are opaque because they have metallic bonding which means that all of the atoms are surrounded by free-moving electrons.

The incident light on metals is absorbed by large numbers of available free electrons in metals to increase their kinetic energy and hence they are opaque.

Which of the following are covalent solids?

1. Iron

2. Diamond

3. Sodium chloride

4. Graphite

Correct Option: B,D
Explanation:

Covalent solids form crystals that can be viewed as a single giant molecule made up of an almost endless number of covalent bonds.

Each carbon atom in diamond and graphite is covalently bound to four other carbon atoms oriented toward the corners of a tetrahedron. Because all of the bonds in this structure are equally strong, covalent solids are often very hard and they are notoriously difficult to melt. Diamond is the hardest natural substance and it melts at $355^oC$.

Hence, the correct options are $B$ and $D$

Passage of current through graphite is due to :

1. free electrons

2. mobile electrons

3. $p\pi-p\pi$ bonded electrons

4. lone pair of electrons

Correct Option: B
Explanation:

In graphite, each carbon atom uses only 3 of its 4 outer energy level electron in covalently bonding to there other carbon atoms in a place. In graphite, electrons are spread out between the structure.

Statement: Diamond glitters because of its high refractive index.

State whether the given statement is true or false
1. True

2. False

Correct Option: A
Explanation:
The diamond glitters because of its high refractive index. The refractive index of diamond is $2.414$.
Higher is the refractive index, the more brilliance a substance has. This is because the substance can bend light rays to a higher degree. The brilliance of the diamond is also dependent on the cut if a diamond which in turn depends on the diamond cutter's skill. Greater number of refractive surfaces result in more glitter.

Hence, the given statement is $\text{true}$
Statement: Increase in pressure in ionic solids may decrease its co-ordination number.

State whether the given statement is true or false.
1. True

2. False

Correct Option: A
Explanation:

Pressure and temperature also influence the structure of ionic solids. The structures of chlorides, bromides and iodides of sodium, potassium and rubidium having $6:6$ Co-ordination at normal temperature and pressure changes to $8:8$ co-ordination like CsCl structure at high pressure, Thus, high pressure increases co-ordination number. Furthermore, CsCl structure changes to NaCl structure at $760$ K. Thus, high temperature decreases co-ordination number.

Hence, the given statement is $true$

Ice is an example of ............ crystal.

1. liquid

2. molecular

3. ionic

4. covalent

Correct Option: B
Explanation:

Molecular Crystals:

In these crystals, molecules occupy the lattice points of the unit cells except in solidified noble gases in which the units are atoms, where the binding is due to van der Waal's forces and dipole-dipole forces. Since van der Waal's forces are non-directional, the structure of the crystal is determined by geometric consideration only.
Ice is the common example in which dipole-dipole forces of attraction (hydrogen bonding) are active. Many organic and inorganic crystals involve hydrogen bonds. Although these are comparatively weaker but play a very important role in determining the structures of substances. Example, polynucleotides, proteins etc.

Hence, the correct option is $\text{B}$

Statement: The melting point of all substances decreases with pressure increase.

State whether the given statement is true or false.
1. True

2. False

Correct Option: B
Explanation:

Melting point increases with increase in pressure. This is because , due to increased pressure molecules tend to remain in solid state. (This is the basic principle on which liquification of gas works)

Hence, the given statement is $false$.

Statement: Ionic solids do not possess molecules.

State whether the given statement is true or false.
1. True

2. False

Correct Option: A
Explanation:

In ionic solids, atoms are present as ions, where cations and anions are arranged in various structure giving rise to a variety of lattices. Thus, they do not have molecules.

Hence, the given statement is $\text{true}$

Dry ice is an example of_________.

1. ionic cystal

2. supercooled liquid

3. molecular crystal

4. covalent crystal

Correct Option: C
Explanation:

Molecular solid is a solid composed of molecules held together by the van der Waals forces. Because these dipole forces are weaker than covalent or ionic bonds, molecular solids are soft and have relatively low melting temperature. Pure molecular solids are electrical insulators but they can be made conductive by doping. Examples of molecular solids include hydrocarbons, ice, sugar, fullerenes, sulfur and solid carbon dioxide.

Assertion (A): Covalent crystals have a higher melting point.
Reason (R): Covalent bonds are stronger than ionic bonds.

1. Both (A) and (R) are correct and (R) is the correct explanation of (A)

2. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

3. (A) is correct but (R) is incorrect

4. (A) is incorrect but (R) is correct

5. Both (A) and (R) are incorrect

Correct Option: A

The cation-anion bond have the largest nature of covalent character for:

1. NaBr

2. SrS

3. CdS

4. BaO

Correct Option: C
Explanation:

More is the deformation in anion, more is the covalent character.
Pseudo inert gas cation e.g. $Cd^{2+}$ causes more polarisation of ion and so, it has higher covalent character.

Which of the following exists as covalent crystals in the solid state?
1. Sulphur

2. Phosphorous

3. Iodine

4. Silicon

Correct Option: D
Explanation:

Covalent crystals are formed by sharing of valence electrons between two atoms resulting in the formation of a covalent bond.

The covalent bonds extend in two or three dimensions forming a giant interlocking structure called network. Diamond and graphite are the good examples of this type
.
Silicon $(Si)$: Covalent solid
Sulphur $(S _8)$: Molecular solid
Phosphorus $(P _4)$ : Molecular solid
Iodine $(I _2)$ : Molecular solid

Network solid among the following is :

1. $Li _{2}O$

2. $SiO _{2}$

3. $H _{2}O$

4. $CO _{2}$

5. $NaCl$

Correct Option: B
Explanation:

A network solid or covalent network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal may be considered a macromolecule. $SiO _2$ is a network solid. $Li _2O$ and $NaCl$ are ionic crystals. $H _2O$ is a covalent liquid and $CO _2$ is a covalent gas.

Which of the following molecules has polar bonds but is a nonpolar molecule?

1. $H _{2}$

2. $H _{2}O$

3. $NH _{3}$

4. $NaCl$

5. $CO _{2}$

Correct Option: E
Explanation:

Carbon dioxide $\displaystyle CO _2$ has polar bonds but is a nonpolar molecule. The structure of $\displaystyle CO _2$  is linear. The individual bond dipoles cancel each other as they point in opposite direction and are equal in magnitude. Hence, the molecule is non polar with zero dipole moment.

$Li (s)$ is:

1. an ionic substance

2. a polar covalent substance

3. a nonpolar covalent substance

4. an amorphous substance

5. a metallic network

Correct Option: E
Explanation:

$Li (s)$ is a metallic solid and has metallic network involving strong metallic bonds. It is crystalline solid formed by atoms of $Li$ metal.

A diamond is an example of this type of solid.

1. Amorphous solid

2. Ionic solid

3. Metallic solid

4. Network covalent solid

Correct Option: D
Explanation:

Covalent-network (also called atomic) solids—Made up of atoms connected by covalent bonds; the intermolecular forces are covalent bonds as well. Characterized as being very hard with very high melting points and being poor conductors. Examples of this type of solid are diamond and graphite, and the fullerenes

In the ionic solid $NH _4NO _3$, ions present are:

1. $NH _4^+$   and $NO^- _3$

2. $N^{5+}, H^+$ and $O^{2-}$

3. $NH _4^-, N^{5+}$ and $O^{2-}$

4. $NH _3, H^+$   and $NO _3^-$

5. $N^{5+}, N^{3-}, H^+$ and $O^{2-}$

Correct Option: A
Explanation:

In the ionic solid ammonium nitrate $NH _4NO _3$,  ions present are ammonium $NH _4^+$   and nitrate $NO^- _3$. Strong electrostatic force of attraction is present between oppositely charged ions.

Salts are the example of:

1. Amorphous solid

2. Ionic solid

3. Metallic solid

4. Molecular solid

Correct Option: B

$I$. Ionic solids have high melting points.
$II$. Molten ionic solids conduct electricity.

1. Statement $I$ is true, Statement $II$ is true

2. Statement $I$ is true, Statement $II$ is false

3. Statement $I$ is false, Statement $II$ is true

4. Statement $I$ is false, Statement $II$ is false

Correct Option: A
Explanation:

Ionic solids are composed of oppositely charged ions(i.e. positively charged cations and negatively charged anions). There is a strong force of attraction because they are oppositely charged. Hence a lot of energy is required to break them due to which they have high melting point.

In molten state, ions are free to move and hence can conduct electricity. That's why molten ionic solid can conduct electricity.

Which type of bonding is responsible for the ability of some solid materials to conduct electricity?

1. Ionic Bonding

2. Metallic Bonding

3. Hydrogen Bonding

4. Covalent Bonding

Correct Option: B
Explanation:

Metallic bonding is responsible for the stability of some solid material to conduct electricity. These bonding have delocalized electrons which act as charge carriers and hence conduct electricity.

Which type of bond does not allow a solid to conduct electricity but will conduct when the substance is in the molten state?

1. Ionic Bonding

2. Metallic Bonding

3. Dipole-Dipole

4. Hydrogen Bonding

Correct Option: A
Explanation:

In the solid-state ionic compounds are held together by strong electrostatic forces. So, the conduction of electricity is not possible. But in the molten state, the ions are free to move and hence conduct electricity.

Which substance exists as a molecular solid at ${20}^{o}C$?

1. ${ CH } _{ 4 }$

2. $Ba{ I } _{ 2 }$

3. ${ H } _{ 2 }O$

4. $P _4$

Correct Option: D
Explanation:

At $20^\circ C$,

A) $CH _4$ is gas.
B) $BaI _2$ is Ionic solid.

C) $H _2O$ is liquid.
D) $P _4$ is molecular solid.

Answer: (D) $P _4$

Which of the following crystalline solids have the highest melting point?

1. Covalent Solids

2. Ionic Solids

3. Molecular Solids

4. Metallic Solids

Correct Option: A
Explanation:
Covalent network solid is a chemical compound in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule

Melting point is high compared to others since melting means breaking covalent bonds (rather than merely overcoming weaker intermolecular forces).

Statement: Covalent solids are good conductor of electricity.

State whether the given statement is true or false

1. True

2. False

Correct Option: B
Explanation:
Covalent compound:
Covalent bonds are formed by sharing of electrons.they don't have a free electron that is required for electricity transfer (electricity is the flow of free electrons!) thus they are bad conductors but ionic compounds are a good conductor because of the presence of free electrons.

Hence, the given statement is false.

Which of the following solids doesn't belong to the class of Covalent solids:

1. Diamond

2. Graphite

3. Silicon Carbide

4. Sodium Chloride

Correct Option: D

Another name for Covalent solids is:

1. Molecular Solids

2. Atomic Solids

3. Element Solids

4. Compound Solids

Correct Option: B
Explanation:

Covalent network solid is a chemical compound in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule.

Another name for covalent solids is Atomic solids.

Separate layers of covalent bonds are present in:

1. Boron carbide

2. Graphite

4. Aluminium nitride

Correct Option: B
Explanation:

Diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Graphite is a crystalline form of carbon and one of the allotropes of carbon. Graphite is the most stable form of carbon under standard conditions. It has a layered, planar structure. The individual layers are called graphene. In each layer, the carbon atoms are arranged in a honeycomb lattice with separation of $0.142 nm,$ and the distance between planes is $0.335 nm.$ Correct answer is option-B.

The major binding force of diamond, silicon and quartz is

1. electrostatic force

2. electrical attraction

3. covalent bond force

4. non-covalent bond force

5. van der Waals' force

Correct Option: C
Explanation:

The major binding force of diamond, silicon and quartz is covalent bond force.
For example, diamond is a covalent solid. It is a big giant network of $\displaystyle sp^3$ hybridised C atoms linked through strong covalent bonds.

If we know the ionic radius ratio in a crystal of ionic solid, what can be known of the following?

1. Magnetic property

2. Nature of chemical bond

3. Type of defect

4. Geometrical shape of crystal

Correct Option: D
Explanation:

Geomatrical shape of crystal can be calculated by knowing the radius ratio in a crystal of ionic solid.

Why is graphite used as a dry lubricant in machinery?

1. Each carbon atom undergoes $sp^{3}$ hybridization in graphite

2. Graphite has layered structure and its cleaves easily between the layers and therefore it is very soft and slippery

3. Graphite is a non-conductor of electricity

4. Graphite has two sigma bonds and two pi bonds

Correct Option: B
Explanation:

Graphite is a mineral made of loosely bonded sheets of carbon atoms, giving it a slippery texture that makes it a very effective lubricant.

Answer: Graphite has a layered structure and its cleaves easily between the layers and therefore it is very soft and slippery.

Which of the following compounds represent represent a normal $2 : 3$ spinel structure?

1. $Mg^{II} Al _{2}^{III}O _{4}$

2. $Co^{II} (Co^{III}) _{2}O _{4}$

3. $Zn(TiZn) O _{4}$

4. $Ni(CO) _{4}$

Correct Option: A,B
Explanation:

In $2:3$ spinel structure                                        General formula is $A^{+2}B _2^{+3}O _4$

$A^{+2} : \cfrac {1}{8}\times Tetrahedral\quad voids$                    $B^{+3} : \cfrac {1}{2} \times Octahedral\quad voids$        $O^{2-}:FCC\quad lattice$

Only $Mg^{+2}Al _2^{+3}O _4$  and  $Co^{2+}(Co^{3+}) _2O _4$ satisfies the above conditions.

$\longrightarrow$ Also, in option (C) $Ti$ have $+4$ oxidtion state.

Ans-(A), (B)

Which type of solid is graphite?

1. Ionic

2. Molecular

3. Metallic

4. Covalent

Correct Option: D
Explanation:

Graphite is covalent solid. Strong covalent bonds are present in between  C atoms in graphite. Another example of a covalent solid is diamond

In a cubic structure of diamond which is made from X and Y, where X atoms are at the corners of the cube and Y at the face centres of the cube. The molecular formula of the compound is
1. $X _2Y$

2. $X _3Y$

3. $XY _2$

4. $XY _3$

Correct Option: D

What is a metallic bonding?

1. The chemical bonding that takes place from the attraction of metal atoms and the surrounding sea of electrons.

2. The chemical bonding that takes place from the attraction of metal atoms and the other elements.

3. The chemical bonding that takes place between metal atoms when they share electrons.

4. The chemical bonding between electrons.

5. The chemical bonding that takes place between metal atoms when they transfer electrons.

Correct Option: E
Explanation:

Metallic bonding: The chemical bonding that takes place from the attraction of metal atoms and the surrounding sea of electrons.
Metallic bonding is the force of attraction between valence electrons and metal ions. It is the sharing of many detached electrons between many positive ions, where the electrons act as a "glue" giving the substance a definite structure. It is unlike covalent or ionic bonding

The electrons and the positive ions in the metal have a strong attractive force between them. Therefore, metals often have high melting or boiling points. The principle is similar to that of ionic bonds.

Hence, the correct option is $\text{E}$

Silicon carbide is a giant molecule having:

1. covalent bond

2. ionic bond

3. molecular bond

4. van der waal bond

Correct Option: A
Explanation:
Electronegativity of silicon $= 1.9$
Electronegativity of carbon $= 2.55$
Electronegativity difference $= 2.55 - 1.9 = 0.65$ (Low) (less than $1.6$)
Hence the bond between $Si$ and $C$ in silicon carbon $(SiC)$ in covalent.

Which of the following have a triclinic system?

1. ${K _2}C{r _2}{O _7}$

2. $N{a _3}Al{F _6}$

3. $NaCl$

4. Quartz

Correct Option: A
Explanation:

Crystal structures of various systems are:

$K _2Cr _2O _7$ - Triclinic

$NaAlF _6$ - Monoclinic

$NaCl$ - Cubic unitcell (Face centered)

Quartz – Triagonal

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