Electrophilic addition of Br₂ to trichloroethene creates a chiral center

Steps:

• Trichloroethene structure: Cl₂C=CHCl, an unsymmetrical alkene.
• Br₂ undergoes electrophilic addition, forming a bromonium ion intermediate on the double bond.
• Anti addition of Br⁻ attacks the CHCl carbon, yielding Cl₂CBr-CHBrCl.
• The CHBrCl carbon has four different substituents (H, Br, Cl, CCl₂Br), making it chiral.

Why A is correct:

• Bromine addition across the C=C bond generates a stereogenic center with four distinct groups, per the definition of chirality in organic molecules.

Why the others are wrong:

• B. HCl: Markovnikov addition gives CCl₃CH₂Cl, with no chiral carbon (all carbons have identical substituents).
• C. NaCN: Nucleophilic substitution or addition yields symmetric or achiral products like CCl₃CH₂CN, lacking a stereocenter.
• D. NaOH: Promotes dehydrohalogenation or hydrolysis to achiral alkenes or alcohols, without forming a chiral center.

Final answer: A