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Q1. Carbon forms compounds with all except:
Helium is a noble gas with a completely filled outer shell (2 electrons in K shell). It is chemically inert and does not form any bonds, whether ionic or covalent. Carbon can form compounds with oxygen (CO, CO₂), nitrogen (cyanides, proteins), and hydrogen (millions of organic compounds). Helium never reacts with carbon because it is already stable and has no tendency to share, gain, or lose electrons.
Q2. Unsaturated compounds contain:
Unsaturated compounds are those in which carbon atoms are bonded by double bonds (C=C) or triple bonds (C≡C). These compounds can add more atoms or groups without removing anything. For example, ethene (C₂H₄) has a double bond, and ethyne (C₂H₂) has a triple bond. Saturated compounds have only single bonds (like methane, ethane). Metallic and ionic bonds are not related to unsaturation.
Q3. Valency of hydrogen is:
Hydrogen has 1 electron in its K shell (electronic configuration 1). It needs 1 more electron to complete its duplet (like Helium). So it can form one bond by sharing its single electron. For example, in H₂, H₂O, CH₄, and HCl, hydrogen always forms one bond. Therefore, the valency of hydrogen is always 1. Valency 2 is for oxygen, 3 for nitrogen, 4 for carbon.
Q4. Covalent bonds have strong forces:
A covalent bond is the strong force of attraction that holds atoms together within a molecule. For example, in a water molecule (H₂O), the O–H bonds are strong covalent bonds. However, the forces between different water molecules (intermolecular forces like hydrogen bonding) are weak. This is why covalent compounds have low melting and boiling points — the weak intermolecular forces break easily, but the covalent bonds within molecules remain strong.
Q5. Property of carbon to form long chains is called:
Catenation is the unique property of carbon atoms to bond with other carbon atoms, forming long chains, branched chains, and rings. Carbon can form single, double, and triple bonds with itself. This property is responsible for millions of organic compounds. Saturation refers to single bonds only, polymerisation is the process of forming polymers from monomers, and isomerism is having the same formula but different structures.
Q6. Graphite consists of layers placed:
In graphite, carbon atoms are arranged in flat hexagonal layers (like honeycomb). These layers are stacked one above the other, but the forces between layers are weak (London forces). This allows the layers to slide over each other easily, making graphite soft and slippery. The layers are not random, side by side, or in circular rings — they are precisely stacked in parallel.
Q7. Silicon shows limited catenation because its compounds are:
Silicon is in the same group as carbon (Group 14) and can also form chains. However, silicon-silicon bonds are weaker and the compounds formed are very reactive. Silicon chains tend to break easily when exposed to air, moisture, or heat. Carbon chains are stable because carbon atoms are smaller and form very strong bonds. So silicon shows only limited catenation, not extensive like carbon.
Q8. Carbon forms stable compounds mainly due to:
Carbon has a very small atomic size (atomic radius about 77 pm). Because of its small size, the nucleus can hold the shared pair of electrons tightly. This results in strong, stable covalent bonds. Large atoms (like silicon or lead) form weaker bonds because the shared electrons are farther from the nucleus. High density and metallic nature are not properties of carbon — carbon is a non-metal with low density.
Q9. In methane, carbon forms bonds with how many hydrogen atoms?
Methane has the molecular formula CH₄. One carbon atom (valency 4) forms four single covalent bonds with four hydrogen atoms (each valency 1). The carbon atom shares its four valence electrons with four hydrogen atoms. So in methane, carbon is bonded to exactly four hydrogen atoms. This gives methane a tetrahedral shape.
Q10. Carbon-carbon bond is:
The carbon-carbon bond is one of the strongest covalent bonds in nature. Because carbon atoms are small, the shared electrons are held very tightly between the two nuclei. The bond energy of a C–C single bond is about 348 kJ/mol, which is very high. This strength allows carbon to form long, stable chains and rings without breaking. Carbon-carbon bonds are not weak, unstable, or temporary.
Q11. Carbon compounds show great diversity because:
The diversity of carbon compounds arises mainly from two properties: catenation (ability to form long chains) and tetravalency (ability to form four bonds). Both properties depend on carbon forming strong covalent bonds. Because the bonds are strong, millions of stable carbon compounds exist. Carbon is not metallic (it is a non-metal), not abundant in the crust (only 0.02%), and not radioactive (except trace amounts of C-14 used in dating).
Q12. Graphite is a good conductor of electricity because:
In graphite, each carbon atom is bonded to only three other carbon atoms. The fourth valence electron is delocalized (free to move) between the layers of graphite. These free electrons can carry an electric current, making graphite a good conductor. Graphite is not metallic (though it conducts like a metal), it is not ionic, and simply being crystalline does not guarantee conductivity (diamond is also crystalline but does not conduct).
Q13. Fullerenes are:
Fullerenes are allotropes of carbon — different structural forms of the same element. The most famous fullerene is C₆₀ (buckminsterfullerene), which has 60 carbon atoms arranged in a hollow sphere resembling a football. Other allotropes of carbon include diamond and graphite. Fullerenes are not ions, not simple rings (they are 3D cages), and not chains.
Q14. Methane is a compound of:
Methane (CH₄) is the simplest hydrocarbon — a compound made of carbon and hydrogen. So methane is primarily a compound of carbon. It is the main component of natural gas, biogas, and CNG. It does not contain oxygen (that would be CO₂ or alcohols), nitrogen (that would be amines), or sulphur (that would be thiols or CS₂).
Q15. In ammonia, nitrogen achieves noble gas configuration by:
Nitrogen has 5 valence electrons (electronic configuration 2,5). It needs 3 more electrons to achieve the stable octet of Neon (2,8). Instead of gaining or losing electrons (which is difficult), nitrogen shares its three electrons with three hydrogen atoms. Each hydrogen shares its one electron. This forms three single covalent bonds (N–H) in ammonia (NH₃), and nitrogen gets a share in 8 electrons.
Q16. In graphite, each carbon atom is bonded to:
In graphite, each carbon atom is covalently bonded to three other carbon atoms in the same hexagonal layer. The bonds are strong and form a flat honeycomb network. The fourth valence electron is delocalized (free) and moves between layers. This is different from diamond, where each carbon is bonded to four other carbon atoms.
Q17. Synthetic diamonds are produced by:
Synthetic diamonds are made in laboratories by subjecting graphite (or carbon) to extremely high pressure (about 50,000 to 100,000 atmospheres) and high temperature (about 1500°C to 2000°C). These conditions mimic the natural process deep inside the Earth where diamonds form. Electric current, dissolving carbon, or simply cooling carbon will not produce diamonds — they will produce graphite or amorphous carbon.
Q18. In diamond, each carbon atom is bonded to:
In diamond, each carbon atom forms four strong covalent bonds with four other carbon atoms. These bonds are arranged in a three-dimensional tetrahedral network. This strong, rigid structure makes diamond the hardest natural substance known. No free electrons are available, so diamond does not conduct electricity.
Q19. How many electrons does each nitrogen atom contribute in the formation of a nitrogen molecule?
Each nitrogen atom has 5 valence electrons. In a nitrogen molecule (N₂), to achieve an octet, each nitrogen atom shares three electrons with the other nitrogen atom. This forms a triple bond (N≡N). So each nitrogen contributes 3 electrons to the bonding. This triple bond is very strong, making nitrogen gas unreactive.
Q20. Synthetic diamonds are:
Synthetic diamonds are chemically identical to natural diamonds — both are pure carbon with the same diamond cubic crystal structure. They have the same hardness, density, and refractive index. Even experts cannot tell them apart without special equipment. They are not chemically different (both are C), not necessarily larger (most are small), and can be colourless just like natural diamonds.
Q21. Graphite is:
Graphite feels smooth and slippery because its hexagonal layers can slide over each other easily. The weak forces between layers allow this movement. This property makes graphite useful as a lubricant and in pencil leads. Graphite is opaque (not transparent), soft (not hard), and not magnetic. Diamond is hard and brittle, but graphite is soft and slippery.
Q22. First fullerene identified was:
The first fullerene discovered in 1985 by Kroto, Curl, and Smalley (Nobel Prize 1996) was C₆₀, named buckminsterfullerene. It contains 60 carbon atoms arranged as 20 hexagons and 12 pentagons, forming a hollow sphere like a football. Later, other fullerenes like C₇₀, C₇₆, and C₈₄ were discovered, but C₆₀ was the first and most studied.
Q23. Diamond is known for being:
Diamond is the hardest natural substance known on Earth. This is because of its three-dimensional network of strong covalent bonds, where each carbon is bonded to four others. This structure cannot be easily scratched or broken. Diamond is not brittle (it is very tough), not a good conductor (it is an insulator), and not soft and slippery (that is graphite).
Q24. Bonds formed by mutual sharing of electrons are called:
A covalent bond is defined as the bond formed when two atoms mutually share one or more pairs of electrons. This was introduced by G.N. Lewis. For example, H₂, O₂, CH₄, and CO₂ have covalent bonds. Metallic bonds involve a sea of delocalized electrons in metals. Ionic bonds involve complete transfer of electrons (e.g., NaCl). Hydrogen bonds are weak attractions between molecules (e.g., in water).
Q25. Molecular formula of ammonia is:
Ammonia is a compound of nitrogen and hydrogen. One nitrogen atom (valency 3) forms three single covalent bonds with three hydrogen atoms (valency 1 each). The correct molecular formula is NH₃. NH₂ is an amide group (unstable as a molecule), N₂H₃ is not a stable compound, and N₃H is not correct. Ammonia is a gas with a sharp smell.
Q26. Arrangement of carbon atoms in graphite is:
In graphite, carbon atoms are arranged in flat hexagonal (six-membered) rings. Each ring looks like a honeycomb. These rings are connected to form large flat sheets or layers. The layers are stacked one above the other. This hexagonal array is what gives graphite its unique properties. Diamond has a cubic lattice, but graphite has a hexagonal layered structure.
Q27. Carbon dioxide has the formula:
Carbon dioxide is formed when one carbon atom (valency 4) shares its electrons with two oxygen atoms (each valency 2). The molecule is linear with double bonds: O=C=O. The formula is CO₂. CO is carbon monoxide (a poisonous gas). C₂O and C₂O₂ are not common stable compounds of carbon and oxygen.
Q28. Methane is a major component of:
Methane (CH₄) is the main component of biogas (about 50-70%) and Compressed Natural Gas (CNG) (about 85-95%). Producer gas contains CO and H₂. Coal gas contains H₂, CO, and CH₄ but methane is not the major component. LPG (Liquefied Petroleum Gas) is mainly propane and butane, not methane. So methane is primarily associated with biogas and CNG.
Q29. Sulphur molecule consists of how many atoms?
The most common and stable form of elemental sulphur at room temperature is the rhombic sulphur molecule, which has eight sulphur atoms arranged in a ring (S₈). The formula is S₈, not just S. Oxygen exists as O₂ (diatomic), but sulphur forms larger ring molecules. Other allotropes of sulphur exist, but the common one is S₈.
Q30. Shape of C₆₀ molecule resembles:
The C₆₀ molecule (buckminsterfullerene) has a shape exactly like a football (soccer ball). It is a hollow sphere made of 20 hexagons and 12 pentagons of carbon atoms. It is not a simple ring (like benzene), not a perfect sphere (it has a pattern), and not a cube. The name “buckyball” comes from this football-like shape.
Q31. The bond formed between two nitrogen atoms in N₂ is:
In a nitrogen molecule (N₂), each nitrogen atom has 5 valence electrons. To achieve an octet, they share three pairs of electrons, forming a triple bond (N≡N). This triple bond is very strong (bond energy about 941 kJ/mol), making nitrogen gas chemically inert. Ionic bonds do not occur between two identical non-metals. Double bonds are in O₂, single bonds in H₂ and Cl₂.
Q32. Bonds present in ammonia molecule are:
Ammonia (NH₃) has three single covalent bonds. Each N–H bond is a single bond formed by sharing one pair of electrons. There are no double or triple bonds in ammonia. The nitrogen atom also has one lone pair of electrons. The bonds are covalent, not ionic. So the correct answer is single bonds.
Q33. Versatile nature of carbon is mainly due to:
The versatile nature of carbon (ability to form millions of compounds) comes from two properties: catenation — carbon atoms can bond with each other to form long chains and rings; and tetravalency — carbon can form four covalent bonds with other atoms (H, O, N, S, Cl, etc.). High density, conductivity, and colour are not special properties of carbon. Diamond and graphite have different densities and colours, but versatility comes from bonding.
Q34. Carbon has a valency of:
Carbon has 4 valence electrons (electronic configuration 2,4). It needs 4 more electrons to complete its octet. It cannot gain or lose 4 electrons easily, so it shares its 4 electrons with other atoms. Therefore, the valency (combining capacity) of carbon is 4. This is why carbon forms four bonds in all its stable compounds, like CH₄, CO₂, and CCl₄.
Q35. Intermolecular forces in covalent compounds are:
In covalent compounds, the forces between molecules (intermolecular forces) are weak — they are either London dispersion forces, dipole-dipole interactions, or hydrogen bonds. Because these forces are weak, covalent compounds generally have low melting and boiling points. For example, methane melts at -182°C. The strong forces are within the molecules (covalent bonds), not between them.
Q36. Low melting and boiling points of covalent compounds are due to:
Covalent compounds have low melting and boiling points because the forces of attraction between their molecules (intermolecular forces) are weak. Only a small amount of heat energy is needed to overcome these forces. Ionic compounds (like NaCl) have high melting points because they have strong electrostatic forces between ions. Presence of ions would increase melting point, not decrease it.
Q37. Saturated compounds have:
Saturated compounds are those in which all carbon atoms are bonded by single covalent bonds. Each carbon atom is attached to the maximum possible number of hydrogen atoms (so they are “saturated” with hydrogen). For example, alkanes like methane (CH₄), ethane (C₂H₆), and propane (C₃H₈) are saturated. Double or triple bonds make compounds unsaturated.
Q38. Different forms of carbon with different physical properties are called:
Allotropes are different structural forms of the same element in the same physical state. Carbon has several allotropes: diamond (three-dimensional network), graphite (hexagonal layers), fullerenes (cage-like molecules), and graphene (single layer). All have the same chemical composition (pure carbon) but different bonding arrangements, leading to different physical properties. Isomers are for compounds with the same formula but different structures.
Q39. Strong carbon bonds are due to:
Carbon atoms are very small. In a covalent bond, the shared electrons are strongly attracted to the nuclei of both carbon atoms. This strong attraction makes the bond very stable and strong. Large atoms form weaker bonds because the shared electrons are farther from the nucleus. Carbon bonds are not ionic, and carbon’s nucleus is not weak — it has 6 protons holding electrons tightly.
Q40. Molecular formula of methane is:
Methane is the simplest hydrocarbon. One carbon atom forms four single bonds with four hydrogen atoms. The molecular formula is CH₄. CH₂ is methylene (unstable), C₂H₆ is ethane, and CH₃ is a methyl group (not a stable molecule by itself). Methane is a colourless, odourless gas and is the main component of natural gas.
Q41. Diamond and graphite differ in:
Both diamond and graphite are made of pure carbon atoms (same chemical composition, same atomic number 6, same valency 4). The difference is in how the carbon atoms are bonded to each other. In diamond, each carbon is bonded to four others in a 3D network. In graphite, each carbon is bonded to three others in flat hexagonal layers. This different bonding arrangement gives them very different physical properties.
Q42. Approximate number of known carbon compounds is:
Over 3 million (three million) carbon compounds are known to science. This is far more than all the compounds of all other elements combined. The exact number keeps growing as new organic compounds are synthesized. This huge number is due to catenation (carbon-carbon bonding) and tetravalency (ability to bond with many other elements).
Q43. Carbon compounds are exceptionally stable due to:
Carbon atoms form very strong covalent bonds with other carbon atoms and with atoms like hydrogen, oxygen, and nitrogen. Because carbon is small, the shared electrons are held very tightly between the nuclei. This makes carbon compounds exceptionally stable. High melting points are a result of stability, not the cause. Carbon compounds are not ionic and do not have weak bonds.
Q44. Fullerene was named after:
Fullerene was named after Richard Buckminster Fuller, an American architect and inventor. He designed geodesic domes (like the one at Epcot Center) that look exactly like the C₆₀ molecule. The name “buckminsterfullerene” honours him. Later, the entire class of such molecules was called “fullerenes” or “buckyballs.” It was not named after a scientist, physicist, or chemist directly, but after an architect.
Q45. Covalent compounds are poor conductors of electricity because:
Covalent compounds do not dissociate into ions when dissolved in water or melted. Without free-moving charged particles (ions or electrons), they cannot conduct electricity. Most covalent compounds are poor conductors. Being solid or having low density is not the reason — some solids (like metals) conduct, and some liquids (like salt solution) conduct. They do not necessarily contain water.
Q46. Carbon is tetravalent because it has:
Tetravalent means having a valency of 4 (ability to form four bonds). Carbon has 4 electrons in its outermost shell (electronic configuration 2,4). It needs 4 more electrons to complete its octet, so it shares its 4 valence electrons. The number of neutrons (6 in C-12) and protons (6) are not directly related to valency. Carbon has only two shells (K and L), not four shells.
Q47. Larger atoms form bonds that are:
Larger atoms have more electron shells, so the outer electrons are farther from the nucleus. When two large atoms form a covalent bond, the shared electrons are not held as tightly because the nucleus has a weaker pull on distant electrons. Therefore, bonds between larger atoms are weaker. For example, the I–I bond in iodine is weaker than the Cl–Cl bond in chlorine because iodine atoms are larger.
Q48. Structure of diamond is:
Diamond has a three-dimensional (3D) network structure. Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. These tetrahedra connect in all directions to form a giant, rigid 3D lattice. This structure makes diamond extremely hard. Graphite has a hexagonal layered (planar) structure, not diamond. Diamond is not linear and not just planar — it extends in all three dimensions.
Q49. Triple bond consists of how many shared pairs of electrons?
A triple covalent bond is formed when two atoms share three pairs of electrons. For example, in a nitrogen molecule (N₂), the bond is N≡N, which means three shared pairs (total 6 electrons). One shared pair = single bond. Two shared pairs = double bond. Three shared pairs = triple bond. Four shared pairs would be a quadruple bond, which is extremely rare and not stable for most elements.