The haloalkanes used in dry-cleaning industries are?

Analyze the question: It asks which haloalkanes (halogenated hydrocarbons) are used as solvents in dry-cleaning.

Concept: Dry-cleaning uses non-aqueous solvents that dissolve grease and oils without damaging fabric. These solvents must be volatile, non-flammable and good at dissolving fats. Chlorinated hydrocarbons fit these requirements.

Going through the options:

• A. Trichloromethane (chloroform) and tetrachloromethane (carbon tetrachloride): Chloroform is mainly known as an old anaesthetic and a laboratory solvent. Carbon tetrachloride was once used for dry-cleaning and in fire extinguishers, but it is toxic and has been phased out. Chloroform is not a dry-cleaning solvent.
• B. Chloroethene and dichloroethene: Chloroethene (vinyl chloride) is the monomer for PVC, not a dry-cleaning solvent.
• C. Trichloroethene and tetrachloroethene: Tetrachloroethene (perchloroethylene, "perc") is the standard dry-cleaning solvent. Trichloroethene is also a degreasing and dry-cleaning solvent. This fits.
• D. Chloroethane and dichloroethene: Chloroethane is used as a local anaesthetic spray and in making tetraethyl lead. It is not used for dry-cleaning.

Note on naming: Strictly speaking, trichloroethene and tetrachloroethene are haloalkenes because they contain C=C bonds. JAMB uses the term "haloalkanes" loosely here.

Answer: C

Exam tip: Link "dry-cleaning" with "perc", which is tetrachloroethene. Then pick the option that contains it. Also remember these uses:

• Chloroform: anaesthetic (historically)
• Carbon tetrachloride: fire extinguishers and old solvent
• Vinyl chloride: PVC
• Tri- and tetrachloroethene: dry-cleaning and degreasing