Railway Science (Chemistry-Carbon And its Compound)

Total Questions: 71

61. What is the valency of carbon in carbon dioxide? [RRB Group D 15/10/2018 (Evening)]

Correct Answer: (b) 4
Solution:

Valency: It refers to the number of bonds an atom can form with other atoms. It depends on the number of outer-shell electrons an atom has available for sharing in covalent bonds.

62. _______ has a very high melting and boiling points. [RRB Group D 29/10/2018 (Morning)]

Correct Answer: (a) Diamond
Solution:

Diamond’s Properties : Pure diamonds are transparent and colourless. It is the impurities that impart colours to them. It has a refractive index of 2.5, which is a very high value.Therefore, it sparkles.

63. The property of carbon due to which its molecules can join with each other to form long carbon chains is called _____. [RRB Group D 30/10/2018 (Afternoon)]

Correct Answer: (d) Catenation
Solution:

This is because C—C bonds are very strong. Down the group the size increases and electronegativity decreases, and, thereby, tendency to show catenation decreases. Carbon (C) is tetravalent in nature so it can form 4 bonds with other atoms.

64. Which of the following allotropes of carbon is used to adsorb colored impurities and bad odors from water and other substances ? [RRB Group D 10/12/2018 (Evening)]

Correct Answer: (b) Charcoal
Solution:

Charcoal is a form of amorphous carbon which shows the property of adsorption. Graphite is a crystalline form of the element carbon. Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Carbon black is obtained by burning hydrocarbons in a limited supply of air.

65. Which allotrope of carbon is used in tools used for cutting glass or mirrors and drilling rocks. [RRB Group D 11/12/2018 (Evening)]

Correct Answer: (c) diamond
Solution:

Diamond is the hardest known substance and is very sharp. Fullerene is an allotrope of carbon wherein its molecules consist of carbon atoms that are connected by single and double bonds.

66. Which isotope of carbon is radioactive and used for radio-carbon dating ? [RRB Group D 12/12/2018 (Afternoon)]

Correct Answer: (a) 14C
Solution:

Carbon-14 dating - The method of age determination that depends upon the decay to nitrogen of radiocarbon (carbon-14). The method was developed in the late 1940s at the University of Chicago by Willard Libby, who received the Nobel Prize in Chemistry for his work in 1960.

67. Two or more elements combine to form a: [RRB ALP Tier - I (13/08/2018) Evening]

Correct Answer: (d) compound
Solution:

Compound is a substance made up of two or more different chemical elements combined in a fixed ratio. Examples - CO₂ (Carbon Dioxide), HO₂ (Hydroperoxyl). Element - An element is a fundamental substance that cannot be broken down into simpler components by any non-nuclear chemical reaction. Examples - H (Hydrogen), He (Helium) and Li (Lithium). Atoms are made up of three subatomic particles that are electrons, protons and neutrons.

68. The number of free electrons in the outermost shell of carbon atoms in diamond is. [RRB ALP Tier - I (13/08/2018) Morning]

Correct Answer: (b) zero
Solution:

Diamond forms a rigid three dimensional network because all four valence electrons of carbon are used in bonding and each carbon has a complete octet. Carbon - Group 14, Atomic Number (6), Recognised as an element by - Antoine Lavoisier (1789), Allotropic form of carbon - Diamond, graphite, Buckminsterfullerene.

69. Which of the following allotropes of Carbon is used as a reducing agent in metallurgy? [RRB ALP Tier - I (13/08/2018) Evening]

Correct Answer: (d) Coke
Solution:

It is a solid black substance that is produced from coal and is burned as a fuel. Uses - Domestic fuel, Production of water gas (CO + H₂) and producer gas (CO + N₂). Charcoal (solid fuel) is an organic carbon compound. It is produced by the incomplete combustion of plant and animal products.
Uses - Fuel in factories and homes to obtain coke, coal gas, and coal tar. Graphite is an allotrope of carbon. Uses - For making lubricants, carbon electrodes, pencils lead, paints and polish.

70. Which of the following is NOT the combined form of carbon ? [RRB ALP Tier - I (13/08/2018) Evening]

Correct Answer: (d) Diamond
Solution:

Carbon is said to exist in a combined state when it is bonded with some other element other than carbon such as oxygen, and calcium in the form of carbonates. Carbon in the Free State is found as diamond and graphite. Limestone, marble and chalk are composed of the compound Calcium Carbonate (CaCO₃). Dolomite (a type of limestone) is an anhydrous carbonate mineral composed of calcium magnesium carbonate [CaMg(CO₃)₂].