14 past paper MCQs on Free Radical Mechanism, from the Chemistry of Hydrocarbons unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.
1.Consider the chlorination of methane. The attack of a chlorine free radical on methane to form a methyl free radical occurs in the: (MDCAT 2022)
Correct answer: (b) propagation step
One radical is consumed and another is produced, which is what keeps the chain going.
2.What is general requirement for free radical substitution reaction of ethane and halogen? (UHS MDCAT 2025)
Correct answer: (d) heat and UV light
Halogenation of an alkane needs heat or ultraviolet light to split the halogen into free radicals.
3.Consider the chlorination of methane to methyl chloride, the attack of chlorine free radical on methane, occurs in which phase? (KMU MDCAT 2025)
Correct answer: (c) Propagation
A chlorine radical attacking methane is a propagation step: a radical is used and another is made.
4.The homolytic fission of C-H bond in an alkane result in (KMU MDCAT 2024)
Correct answer: (a) Alkyl free radical
Homolysis gives each atom one electron of the pair, leaving an alkyl free radical.
5.The carbon atom carrying positive charge and attached to three other atoms or groups is called (KMU MDCAT 2024)
Correct answer: (c) Carbocation
A positively charged carbon with three attachments is a carbocation.
6.Consider the chlorination of methane, the attack of chlorine free radical on methane form methyl free radical occurs in ? (UHS MDCAT 2023)
Correct answer: (b) Propagation step
A radical is used and another is made, which is the mark of a propagation step.
7.Halogenation of alkane in sunlight is an example of: (PMC MDCAT 2022)
Correct answer: (c) Substitution reaction
A hydrogen of the alkane is replaced by a halogen, which is substitution.
8.The termination step of the Halogenation of alkanes in the presence of sunlight involves the formation of: (PMC MDCAT 2022)
Correct answer: (d) Molecules
Two radicals meeting join into a molecule, and the chain ends there.
9.Free radical reactions take place in the presence of ______? (PMC Practice 2021)
Correct answer: (b) Sunlight
Ultraviolet light splits the halogen into radicals and the chain begins.
10.The species which are produced by heterolytic bond breaking and can act as electron pair donors are known as: (UHS MDCAT 2018)
Correct answer: (a) Nucleophiles
A species with a lone pair to give is a nucleophile.
11.Reaction mechanism of alkanes with halogens is known as; (UHS MDCAT 2018)
Correct answer: (b) Free radical substitution
Halogenation of an alkane goes by free radicals, and a hydrogen is substituted.
12.Chlorination and Bromination mostly uses: (UHS MDCAT 2017)
Correct answer: (d) U.V. light
Ultraviolet light splits the halogen molecule into radicals and the chain begins.
13.Among the following, which one is a nucleophile; (UHS MDCAT 2017)
Correct answer: (b) OH-
The hydroxide ion has a lone pair to give, so it is a nucleophile.
14.. Which one of the following is NOT a nucleophile: (UHS MDCAT 2016)
Correct answer: (c) BF3
Boron trifluoride has an empty orbital and accepts a pair, so it is an electrophile.