H2 and Cl2 do not react in the dark, but in the presence of light a vigorous reaction is initiated due to the formation of:
Correct answer: B. Chlorine free radical
- A. Hydrogen free radical
- B. Chlorine free radical
- C. Hydrogen chloride molecule
- D. Both hydrogen and chlorine free radicals
Explanation
To break the covalent bond between two chlorine atoms, photons of ultraviolet rays are required. There is no such requirement for breaking the bond between hydrogen atoms, hence the answer is B.
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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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