Free Radical Chain Reaction Steps:

• Identify reactions involving initiation (radical formation), propagation (radical chain), and termination (radical recombination).
• Examine each equation for halogenation, a classic free radical process.
• Rule out ionic or nucleophilic substitutions lacking chain steps.
• Confirm A matches radical chlorination of alkanes.

Why A is correct:

• Chlorination of ethyl chloride (or alkane analog) follows free radical mechanism with Cl• initiation by light/heat, propagation via H-abstraction and Cl-addition, and termination by radical coupling, per chain reaction theory.

Why the others are wrong:

• B: Nucleophilic substitution (SN2) of alkyl bromide with OH⁻, no radicals.
• C: Acid-catalyzed SN1/SN2 conversion of alcohol to bromide, ionic mechanism.
• D: Unclear reaction (possibly cyanohydrin, but invalid for alcohol); lacks chain steps.

Final answer: A