Asked in PMC Practice Test 34 (2021) 2021

Free radical reactions take place in the presence of _.

Correct answer: B. Sun light

  • A. Heat
  • B. Sun light
  • C. Catalyst
  • D. Oxygen

Explanation

Option B is correct since sunlight is simply a source of energy, and is being used to break bonds. Option A is incorrect since heat results in the formation of free radicals and enables the beginning of a free radical chain reaction referred to as Initiation. Option C is incorrect since the catalyst is the process of increasing the rate of a chemical reaction. Option D is incorrect since free radical reactions take place in the presence of sunlight, not oxygen.

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About Free Radical Substitution

Free radical substitution explains how alkanes react with halogens under ultraviolet light or heat through initiation, propagation and termination steps. The mechanism involves homolytic bond fission and radical intermediates, while product formation depends on the relative stability of radicals and differs from ionic substitution.

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