Anti-freeze used in a vehicle radiator is a mixture of water and

Analyze the question: Anti-freeze is added to the water in a car radiator to lower the freezing point of the coolant, so it doesn't freeze in cold conditions (and it also raises the boiling point).

Concept: The standard anti-freeze is ethane-1,2-diol (ethylene glycol), a dihydroxy alcohol (diol). It dissolves in water through hydrogen bonding, and this lowers the freezing point (a colligative property). It's also not very volatile, so it doesn't evaporate easily from a hot radiator.

Checking the options:

• A. Propanetriol (glycerol/glycerine): A polyhydric alcohol with three -OH groups. It is miscible with water, has a high boiling point, and lowers the freezing point of water. It is the closest option to the real anti-freeze, which is a polyhydric alcohol.
• B. Propanol: A monohydric alcohol. It is volatile and flammable, so it is not suitable for a hot radiator.
• C. Propanone (acetone): Very volatile and highly flammable, so it is unsuitable.
• D. Propanal: An aldehyde, volatile and reactive, so it is not used.

Of the choices given, the only polyhydric alcohol (like ethane-1,2-diol) is propanetriol. Glycerol has also been used as an anti-freeze, and the others are volatile and flammable.

Exam tip: Remember "anti-freeze = polyhydric alcohol (diol/triol)". If you see ethane-1,2-diol, pick it. If it's not there, choose the option with multiple -OH groups. Also remember: glycerol (propane-1,2,3-triol) is used in soaps, explosives (nitroglycerine), and cosmetics.