Here below some basic MCQ’s about “Alkanes, Alkenes, Alkynes and Aromatic Hydrocarbons” which is well explained. Let’s check one by one which is given below.
1. Which of the following is the correct IUPAC name of the compound CH3-CH=CH-CH3?
a) 1-Butene
b) But-2-ene
c) 2-Butyne
d) 1-Butyne
Answer: b) But-2-ene
Explanation: The correct IUPAC name is But-2-ene because it is a four-carbon chain (butane) with a double bond between the second and third carbon atoms. The position of the double bond is indicated by the number 2.
2. Which of the following reactions is used to convert an alkene into an alkane?
a) Combustion
b) Hydrogenation
c) Dehydrohalogenation
d) Oxidation
Answer: b) Hydrogenation
Explanation: Alkenes are converted to alkanes by the process of hydrogenation, where hydrogen gas (H₂) is added across the double bond of the alkene in the presence of a metal catalyst like Pt, Pd, or Ni.
3. Which reagent is commonly used for the bromination of alkanes?
a) Br₂/FeBr₃
b) Br₂/UV light
c) HBr
d) Br₂/AlBr₃
Answer: b) Br₂/UV light
Explanation: The bromination of alkanes takes place through a free radical mechanism when Br₂ is exposed to UV light, leading to the formation of brominated alkanes.
4. Which of the following compounds does not show geometrical isomerism?
a) 1-Butene
b) 2-Butene
c) 1,2-Dichloroethene
d) 1-Pentene
Answer: a) 1-Butene
Explanation: 1-Butene does not show geometrical isomerism because the double bond is at the terminal position, leaving no possibility for different spatial arrangements of substituents around the double bond.
5. Which of the following is an example of an aromatic hydrocarbon?
a) Ethane
b) Propene
c) Benzene
d) Butyne
Answer: c) Benzene
Explanation: Benzene is an example of an aromatic hydrocarbon because it has a cyclic structure with alternating double and single bonds, which satisfies Huckel’s rule for aromaticity (4n+2 π electrons).
6. Which of the following alkenes undergoes polymerization most readily?
a) Propene
b) Ethene
c) Butene
d) Pentene
Answer: b) Ethene
Explanation: Ethene (C₂H₄) is the simplest alkene and undergoes polymerization easily to form polyethylene, a widely used polymer.
7. What is the product formed when ethyne (acetylene) reacts with hydrogen chloride?
a) Vinyl chloride
b) Ethyl chloride
c) Ethene
d) Chloroethane
Answer: a) Vinyl chloride
Explanation: Ethyne reacts with HCl to form vinyl chloride (CH₂=CHCl) through the addition of HCl to the triple bond, resulting in a double bond product.
8. Which of the following compounds is the most reactive towards electrophilic substitution reactions?
a) Benzene
b) Toluene
c) Nitrobenzene
d) Phenol
Answer: d) Phenol
Explanation: Phenol is the most reactive towards electrophilic substitution due to the electron-donating effect of the hydroxyl group (-OH), which increases the electron density on the benzene ring, especially at the ortho and para positions.
9. Which of the following statements about alkynes is correct?
a) Alkynes are more reactive than alkenes in electrophilic addition reactions.
b) Alkynes can undergo hydrogenation to form alkenes.
c) Alkynes are generally less acidic than alkanes.
d) Alkynes undergo nucleophilic addition more readily than alkenes.
Answer: b) Alkynes can undergo hydrogenation to form alkenes.
Explanation: Alkynes can be partially hydrogenated to form alkenes by adding hydrogen (H₂) in the presence of a catalyst such as Lindlar’s catalyst.
10. Which of the following processes leads to the formation of an aromatic compound?
a) Cracking of hydrocarbons
b) Dehydrocyclization
c) Halogenation of alkanes
d) Polymerization of alkenes
Answer: b) Dehydrocyclization
Explanation: Dehydrocyclization is a process in which alkanes are converted into aromatic compounds, such as the conversion of hexane to benzene, by removing hydrogen and forming a cyclic structure.
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