Bis-chloromethyl ether is a carcinogen that can be chemically formed by a reaction between formaldehyde and hydrochloric acid. Which pair forms it?

• A. Formaldehyde and acetic acid
• B. Formaldehyde and hydrochloric acid
• C. Water and oxygen
• D. Methanol and sulfuric acid

Answer: (B)

Bis-chloromethyl ether forms when a formaldehyde molecule encounters a chloride source in strongly acidic conditions, allowing chlorine atoms to attach to the two ends of the chloromethyl groups and be connected through an ether oxygen. Formaldehyde supplies the CH2O carbon backbone, while hydrochloric acid provides the chloride needed to create the chloromethyl groups (CH2Cl) that link via oxygen to form the bis-chloromethyl ether structure, CH2Cl–O–CH2Cl. The other pairings lack the chloride source or the reactive formaldehyde chloride chemistry needed to assemble this specific chloromethyl ether, so they don’t produce BCME.