(3)

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.

(2)

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.

(1)

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.

(3)

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.

(2)

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.

(2)

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

(1)

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.