NON-MEATALS, A . Carbon and its Various Forms

1. Which one of the following elements forms the maximum number of compounds? [U.P. P.C.S. (Mains) 2016]

(a) Hydrogen
(b) Carbon
(c) Nitrogen
(d) Oxygen

Correct Answer: (b) Carbon

Solution:Among the above elements, carbon forms the maximum number of compounds. Carbon forms an extraordinarily vast number of compounds due to its unique ability to catenate (form long chains and rings with itself) and its tetravalency, allowing it to bond with a wide variety of other elements. This leads to the immense field of organic chemistry.

2. Which of the following do not consist carbon? [42nd B.P.S.C. (Pre) 1997]

(a) Diamond
(b) Graphite
(c) Coal
(d) None of these

Correct Answer: (d) None of these

Solution:Diamond is an additional form (allotrope) of carbon. Its relative density is 3.5. Graphite is a slaty-black colored smooth and brightly organic matter of relative density 2.25, which is also an allotrope of carbon, while coal is a solid carbon-containing organic matter used as fuel. Thus, all of the three consist of carbon.

3. Graphite and diamonds are basically made up of atoms of: [Chhattisgarh P.C.S. (Pre) 2023]

(a) Silica
(b) Carbon
(c) Nitrogen
(d) None of the above

Correct Answer: (b) Carbon

Solution:Diamond and graphite are different forms of carbon, known as allotropes. This means they are made of the same element (carbon) but have different structures. Diamond has a tetrahedral crystal structure, while graphite has a layered structure.

4. Thermodynamically the most stable form of carbon is: [U.P. P.C.S. (Pre) 2022]

(a) Fullerenes
(b) Diamond
(c) Coal
(d) Graphite

Correct Answer: (d) Graphite

Solution:Thermodynamically, the most stable form of carbon is graphite. Graphite has a high melting point, modest thermal expansion, and high specific heat, making it relevant for composites and structural materials and as heat shields in certain applications, including nuclear reactors. Graphite consists of layers of carbon sheets (graphene sheets) that are only weakly bonded with each other, causing great anisotropy in the material.

5. Which of the following statements about graphite and diamond is true? [67th B.P.S.C. (Pre) 2022]

(a) They have the same crystal structure
(b) They have the same hardness
(c) They have the same electrical conductivity
(d) They can undergo the same chemical reaction
(e) None of the above/More than one of the above

Correct Answer: (d) They can undergo the same chemical reaction

Solution:Graphite and diamond are both composed of carbon (C), but physically, they are very different. The differing physical properties of graphite and diamond arise from their distinct crystal structures. In a diamond, the carbon atoms are arranged tetrahedrally. The carbon atoms in graphite are also arranged in an infinite array but layered in trigonal planar. Another important difference is their hardness. Graphite is very soft (Mohs hardness of 1 to 2), while diamonds are the hardest known natural substance (Mohs hardness of 10). Diamond is an insulator, while graphite is a conductor of electricity. Despite extreme differences in physical properties, diamond and graphite are chemically the same and can undergo the same chemical reactions.

6. Which of the following statements about diamond and graphite is true? [68th B.P.S.C. (Pre) 2022]

(a) They have the same electrical conductivity
(b) They have the same crystal structure
(c) They have the same degree of hardness
(d) More than one of the above
(e) None of the above

Correct Answer: (e) None of the above

Solution:Graphite and diamond are both composed of carbon (C), but physically, they are very different. The differing physical properties of graphite and diamond arise from their distinct crystal structures. In a diamond, the carbon atoms are arranged tetrahedrally. The carbon atoms in graphite are also arranged in an infinite array but layered in trigonal planar. Another important difference is their hardness. Graphite is very soft (Mohs hardness of 1 to 2), while diamonds are the hardest known natural substance (Mohs hardness of 10). Diamond is an insulator, while graphite is a conductor of electricity. Despite extreme differences in physical properties, diamond and graphite are chemically the same and can undergo the same chemical reactions.

so, none of the above option is true.

7. In the context of lab-grown diamonds (LGDs), what is used as a diamond seed? [69th B.P.S.C. (Pre) 2023]

(a) White sapphire
(b) Moissanite
(c) Graphite
(d) Cubic zirconia (CZ)

Correct Answer: (c) Graphite

Solution:In the context of lab-grown diamonds, the seed is a small diamond fragment or a carbon source (mainly graphite). Diamond structure can be produced by applying high temperature and pressure, with catalysts such as chromium, iron, or platinum. White sapphire (aluminum oxide) cannot form diamond, which is pure carbon. There are two main lab-grown diamond production methods: high pressure/high temperature (HPHT) and chemical vapor deposition (CVD). CVD is more popular for producing gem-quality diamonds for jewelry, while HPHT is more often used for industrial diamonds.

8. Arrange the following substances in chronological order of their first synthesis in the lab: [U.P.P.C.S. (Pre) 2019]

Black gold
Fullerene
Graphene
Kevlar

Select the correct answer from the codes given below:

(a) 1,2,3,4
(b) 4,2,3,1
(c) 2,4,3,1
(d) 4,1,2,3

Correct Answer: (b) 4,2,3,1

Solution:Kevlar is a heat-resistant, strong synthetic fiber developed by Stephanie Kwolek at Dupont Lab (USA) in 1965.

Fullerene was first discovered in 1985 by British scientist Harold Kroto and American scientists Richard E. Smalley, James R. Heath, and Robert F. Curl Jr.

Graphene, an allotrope of carbon, was first isolated and synthesized in 2004 by Andre Geim and Konstantin Novoselov at the University of Manchester.

In 2019, scientists at the Tata Institute of Fundamental Research (TIFR) developed 'black gold' using gold nanoparticles, which has unique properties such as light and carbon dioxide absorption.

Chronological order: Kevlar (1965) -> Fullerene (1985) -> Graphene (2004) -> Black gold(2019)

9. Which of the following is made up of carbon only? [U.P.P.C.S. (Mains) 2015]

(a) Kevlar
(b) Lexan
(c) Graphene
(d) Spider silk

Correct Answer: (c) Graphene

Solution:Graphene is an allotrope of Carbon in the form of a single layer of atoms in a two-dimensional hexagonal lattica which one atom forms each vertex. Thus, it is a nano structure of carbon atoms. It is the basic structural element of other allotropes including Graphite, Charcoal, Carbon nanotubes and Fullerenes. Graphene is a form of Carbon nanostructure

10. Graphene is — [U.P. P.C.S. (Pre) 2018]

(a) An alloy of carbon
(b) Nano structure of carbon
(c) Isotope of carbon
(d) None of the above

Correct Answer: (b) Nano structure of carbon

Solution:Graphene is an allotrope of Carbon in the form of a single layer of atoms in a two-dimensional hexagonal lattica which one atom forms each vertex. Thus, it is a nano structure of carbon atoms. It is the basic structural element of other allotropes including Graphite, Charcoal, Carbon nanotubes and Fullerenes. Graphene is a form of Carbon nanostructure.