Free-radical chlorination of alkanes

Steps:

• Diffuse sunlight initiates free radicals by breaking Cl-Cl bond without high UV intensity.
• Ethane (C2H6) reacts via substitution, where Cl replaces H to form chloroethane (C2H5Cl).
• Mechanism involves initiation, propagation (Cl• abstracts H•, forming HCl; then Cl2 forms C2H5Cl•), and termination.
• No gaseous byproducts evolve separately, as HCl integrates into the mixture.

Why B is correct:

• Free-radical substitution produces alkyl chloride without gas evolution, per the propagation step: C2H6 + Cl• → C2H5• + HCl (HCl not released as distinct gas).

Why the others are wrong:

• A: HCl forms but is not "given off" as a separate gas in standard conditions.
• C: Hydrogen gas is not produced; substitution yields HCl, not H2.
• D: Nucleophilic substitution applies to halides, not alkanes like ethane.

Final answer: B