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Carbon exists in the atmosphere in the form of carbon dioxide gas $\left(C{O}_2\right)$in air (Only 0.03%) and in the earth crust it exists in the form of the minerals like carbonates. It also occurs in the form of fossil fuels, organic compounds, wood, cotton and wool, etc.

(4)

Covalent compounds are held together by weak intermolecular forces which fails to hold the compound bind tightly. Thus, a small amount of heat energy is capable of breaking these weak intermolecular forces, therefore, the melting and boiling points of covalent compounds is low. Covalent compounds are non-polar in nature which means they do not dissolve in water, instead make a separate layer on the water’s surface. Hence, covalent bonds are insoluble in water. Covalent compounds are formed by the sharing of electron in the bonding atoms between two non-metals.

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Electricity results from motion of electrons or ions. Most carbon compounds are poor conductors of electricity because they are formed by the sharing of electrons and therefore, they do not have free electrons. On dissolving them in water they do not form ions. So, they are generally poor conductors of electricity. Force of attraction between molecules of carbon compounds is not very strong because they form covalent bond by sharing their valence electron in order to attain stable electronic gas configuration.

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Catenation is the property of self-linking of an element by which an atom combines with the other atoms of the same element to form long chains. This property is exhibited by carbon as it forms covalent bonds with other carbon atoms to form longer chains and structures. This is the reason for the presence of the vast number of organic compounds in nature.

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Buckminsterfullerene (C60) is an allotropic form of carbon. It has carbon atoms arranged in the form of football and due to their resemblance with football they are also known as Bucky balls.

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Buckminsterfullerene is the first discovered fullerene. It is a molecule of carbon in the form of a soccer ball consisting of 60 C-atoms and is having the formula C60. These 60 carbon atoms are joined together by strong covalent bonds and are arranged in interlocking hexagonal and pentagonal rings of carbon atoms.

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The allotrope of carbon which is a good conductor of heat and electricity is graphite. This is because, in its planar structure it has three electrons which are covalently bonded and fourth electron is free to move along the layers from one carbon atom to the next when connected to an external battery.

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In diamond, each carbon atom is bonded to four other carbon atoms tetrahedrally to form a rigid three-dimensional structure. This rigid three-dimensional structure of carbon is responsible for the hardness and rigidity of diamond

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Carbon is found in many forms in nature which differ from each other in various physical properties but they exist in same state. These forms of carbon are known as allotropes of carbon. From the given options, fullerene, diamond, graphite are all different types of allotropes. Whereas, fluorine is a non-metal which belongs to halogen family. Hence, fluorine is not an allotrope of carbon.

(4)

Diamond is the hardest substance known, this is due to its structure in which carbon atoms are arranged in a lattice giving it a giant covalent structure with great forces of attraction. Diamond has high thermal conductivity, this is due to the stiff chemical bonds between the carbon atoms. It has high refractive index which gives it the transparency and brilliance and it is bad conductor of electricity because of the absence of free mobile electrons.

(3)

Organic compounds have low melting and boiling points because they are made of weak covalent bonds. Thus, the property which is not true regarding organic compounds is that they have high melting and boiling points.

(4)

Carbon as a group 14 element, has four electrons in its outer shell. Carbon typically shares electrons to achieve a complete valence shell, forming bonds with multiple other atoms.

(2)

The electronic configuration of carbon (C) is 2, 4. To complete its octet, it will share its 4 valence electrons with hydrogen atom and form $CH₄$ molecule. As carbon is sharing its 4 valence electrons, it will form four covalent bonds.
Now, the electronic configuration of C in $CH₄$ is 2, 8.
Electronic configuration of Ne (atomic number = 10) is 2, 8. Hence, after the formation of four covalent bonds, carbon attains the electronic configuration of Neon.

(1)

The term isomerism refer to the organic compounds with same molecular formula but different structural formulae. An example is the compound with the molecular formula $C_5{H}_{12}$. It has three isomers: n-pentane, isopentane and neopentane which differ from each other in their structure but they have same molecular formula.

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Since, branching is not possible with carbon 1, 2, 3 so the minimum number of the carbons required by the hydrocarbon to show isomerism is four.

(3)

Structural formula of pentane is:

Number of C - C covalent bonds = 4

Number of C - H covalent bonds = 12

Hence the total number of covalent bonds in the structure of pentane is 16.

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Isomerism is a phenomenon in which two or more compounds have the same chemical formula but possess different structural formulae. Pentane is an organic compound and an alkane with molecular formula $C_5{H}_{12}$. There are five carbons in its structure which can be arranged in three different ways to form 3 different structural isomers of pentane. These are n-pentane, iso-pentane and neo-pentane.

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$C{H}_4, C_2{H}_6, C_3{H}_8$ are all saturated carbon compounds with general formula $C_n{H}_{2n+2}$ whereas $C_4{H}_8$ is an alkene with general formula $C_n{H}_{2n}.$ Thus, $C_4{H}_8$ does not belong to the same homologous series as it is an alkene.

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Homologous series is the series comprising of compounds that share same chemical properties and functional groups. Alkynes have general formula,$C_n{H}_{2n-2}$, where n is number of carbon atoms.

Thus, from the given options, $C_3{H}_4$ belongs to the homologous series of alkynes.

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A homologous series is a family of compounds with the same general formula, same functional group and similar chemical properties. Each family of organic compound is called a homologous series for example,

Homologous series of Alkanes with general formula $C_n{H}_{2n+2}$

Homologous series of Alkene with general formula $C_n{H}_{2n}$

Homologous series of Alkyne with general formula $C_n{H}_{2n-2}$

Hence, from the general formula of the homologous series of alkanes, this can be confirmed that $C_3{H}_8$ belongs to the homologous series of alkanes.

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The first member of the alkyne family is ethyne $\left(C_2{H}_2\right)$, with two carbon atoms bonded by a triple bond. It is a hydrocarbon and the simplest alkyne. Its molecular weight is 26.04 g/mol.

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In homologous series, the two consecutive members will differ by $CH₂$ unit or 14 amu.
The molecular masses of first three members of alkanes with general formula $CₙH₂ₙ₊₂$ are shown below:
Methane $(CH₄)$ = 16 amu
Ethane $(C₂H₆)$= 30 amu
Propane $(C₃H₈)$ = 44 amu
From the above examples, it is clear that atomic mass unit of successive members of a homologous series vary by 14 amu.

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A double covalent bond is formed when two pairs of electrons are shared between them. For example, in an oxygen molecule, there is a double bond between two oxygen atoms as they share two pairs of electrons i.e., 4 electrons.

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A hydrocarbon is an organic chemical compound composed exclusively of hydrogen and carbon atoms. For example, the simplest hydrocarbon is methane molecule with the molecular formula $C{H}_4$

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The bond between two identical non-metallic atoms has a pair of electron equally shared between them. This is due to the equal sharing of electrons between the bonded atoms. Hence, the bonded atoms will hold on the shared pair of electrons.

(1)

Hydrocarbons undergo complete combustion when a sufficient amount of oxygen is available. During the complete combustion of hydrocarbons, carbon dioxide and water are formed.

The equation for the combustion of a hydrocarbon in air can be represented as:

Fuel + Oxygen → Water + Nitrogen + Carbon dioxide

Example:
$C{H}_4 + 2O_2 \to 2H_{2}O + C{O}_2$

(1)

There are four single bonds present in methane as 4 hydrogen atoms satisfy the carbon valency 4 which can be represented as shown in the figure: