Option 1: Propyl alcohol is not typically used as an anti-freeze. It`s a type of alcohol, but it`s not specifically designed for this application.

Option 2: Ethanol, also a type of alcohol, is sometimes used in small amounts to prevent fuel-line freeze-up in cars, but it isn`t the primary compound used for anti-freeze.

Option 3: Methanol, another type of alcohol, is also sometimes used as an anti-freeze. But, like ethanol, it isn`t the main compound utilized for this purpose.

Option 4: Ethylene glycol is the correct answer. This compound is the most common active ingredient in-engine coolant and antifreeze solutions. It has a low freezing point and high boiling point, making it excellent at regulating engine temperature and preventing freezing or overheating. It is specifically designed for this application.