Organic Chemistry A. Hydrocarbons

1. Which one of the following is the correct sequential order in which these appeared under simulated primitive earth condition? [I.A.S. (Pre) 1994]

(a) Methane, Hydrogen Cyanide, Nitrile, Amino Acid
(b) Hydrogen Cyanide, Methane, Nitrile, Amino Acid
(c) Amino Acid, Nitrile, Hydrogen Cyanide, Methane
(d) Nitrile, Amino Acid, Methane, Hydrogen Cyanide

Correct Answer: (a) Methane, Hydrogen Cyanide, Nitrile, Amino Acid

Solution:The correct sequence of their appearance under simulated primitive earth conditions is Methane, Hydrogen Cyanide, Nitrile, Amino Acid.

2. Which is the fundamental element of all organic compounds? [56th to 59th B.P.S.C. (Pre) 2015 ,U.P.U.D.A./L.D.A. (Pre) 2001]

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

Correct Answer: (c) Carbon

Solution:

Carbon is the fundamental element of all organic compounds (including bio-compounds). Organic compounds are a large class of chemical compounds in which one or more atoms of carbon are covalently linked to atoms of other elements, most commonly hydrogen, oxygen, or nitrogen.

3. In all bio-compounds the most necessary fundamental element is — [U.P.P.C.S. (Mains) 2015]

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

Correct Answer: (b) Carbon

Solution:

Carbon is the fundamental element of all organic compounds (including bio-compounds). Organic compounds are a large class of chemical compounds in which one or more atoms of carbon are covalently linked to atoms of other elements, most commonly hydrogen, oxygen, or nitrogen.

4. Which one of the following sets of elements was primarily responsible for the origin of life on the Earth? [I.A.S. (Pre) 2012]

(a) Hydrogen, Oxygen, Sodium
(b) Carbon, Hydrogen, Nitrogen
(c) Oxygen, Calcium, Phosphorus
(d) Carbon, Hydrogen, Potassium

Correct Answer: (b) Carbon, Hydrogen, Nitrogen

Solution:Biologists consider that six elements were primarily responsible for the origin of life on Earth: Hydrogen, Oxygen, Carbon, Nitrogen, Phosphorus, and Sulphur. The matter within every living earthly creature mainly consists of these chemical compounds, e.g., protein, nucleic acid, carbohydrates, vitamins, hormones, etc.

5. Which one of the following is the correct sequence in increasing order of molecular weights of the hydrocarbons? [I.A.S. (Pre) 2001]

(a) Methane, Ethane, Propane, and Butane
(b) Propane, Butane, Ethane, and Methane
(c) Butane, Ethane, Propane, and Methane
(d) Butane, Propane, Ethane, and Methane

Correct Answer: (a) Methane, Ethane, Propane, and Butane

Solution:The increasing order of atomic weight of hydrocarbons is: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), Butane (C₄H₁₀).

6. A hydrocarbon in which two carbon atoms are joined by a double bond is called as an: [63rd B.P.S.C. (Pre) 2017]

Correct Answer: (b) Alkene

Solution:A hydrocarbon in which two carbon atoms are joined by a double bond is called an alkene. Alkenes have the general formula

C_{n} H_{2 n}

. They are also known as olefins.

7. Arrange the following carbon compounds in decreasing order of their melting points: [Chhattisgarh P.C.S. (Pre) 2022]

(a) Ethanol > Chloroform > Acetic acid > Methane
(b) Chloroform > Acetic acid > Ethanol > Methane
(c) Acetic acid > Chloroform > Methane > Ethanol
(d) Acetic acid > Chloroform > Ethanol > Methane

Correct Answer: (d) Acetic acid > Chloroform > Ethanol > Methane

Solution:The correct decreasing order of melting points is:
Acetic acid (about 16.6°C) > Chloroform (about -63.5°C) > Ethanol (about -114.1°C) > Methane (about -182.5°C).

8. Which of the following gases is used in cigarette lighters? [56th to 59th B.P.S.C. (Pre) 2015]

(a) Butane
(b) Methane
(c) Propane
(d) Radon

Correct Answer: (a) Butane

Solution:Butane is a flammable hydrocarbon with the molecular formula C₄H₁₀. It is commonly used as fuel in cigarette lighters.

9. Leakage of which of the following gases had caused the Bhopal Gas Tragedy? [Uttarakhand P.C.S. (Pre) 2012]

(a) Methyl isocyanate
(b) Carbon monoxide
(c) Nitric oxide
(d) Sulphur dioxide

Correct Answer: (a) Methyl isocyanate

Solution:The Bhopal Gas Tragedy resulted from an accident that occurred on the night of December 2-3, 1984. The plant released 42 tonnes of methyl isocyanate (MIC) gas, exposing more than 500,000 people to toxic gases.

10. Bhopal Gas Tragedy was caused due to the leakage of: [U.P.P.C.S. (Pre) 2017]

(a) Methyl isocyanate
(b) Nitrogen dioxide
(c) Sulphur dioxide
(d) Carbon monoxide