Antifreeze is a substance that is added to the cooling system of an engine to lower the freezing point of the liquid coolant. It prevents the coolant from freezing in cold temperatures and also raises the boiling point to prevent overheating. The antifreeze mixture is typically made up of a combination of water and an organic compound called ethylene glycol or propylene glycol.

The correct answer to the given question is option 'B' - C2H5OH (ethanol). Ethanol is not commonly used as the primary component of antifreeze, but it can be added in small amounts to enhance the performance of the coolant. Here's an explanation of why ethanol can be used in antifreeze mixture:

1. Ethanol has a lower freezing point than water: Ethanol has a freezing point of approximately -114 degrees Celsius (-173 degrees Fahrenheit), which is significantly lower than the freezing point of water (0 degrees Celsius or 32 degrees Fahrenheit). By adding ethanol to the antifreeze mixture, the overall freezing point of the coolant can be lowered, providing better protection against freezing in extremely cold temperatures.

2. Ethanol helps to prevent corrosion: Ethanol has properties that help to inhibit corrosion in the cooling system. It acts as a corrosion inhibitor, protecting the metal components of the engine from rust and other forms of corrosion. This can help to extend the lifespan of the cooling system and prevent damage to the engine.

3. Ethanol is compatible with other antifreeze components: Ethanol can be mixed with other antifreeze components, such as ethylene glycol or propylene glycol, without causing any chemical reactions or adverse effects. This makes it a suitable additive for antifreeze mixtures.

4. Ethanol is readily available: Ethanol is a widely available and relatively inexpensive substance, making it a practical choice for use in antifreeze mixtures.

Overall, while ethanol is not commonly used as the primary component of antifreeze, it can be added in small amounts to enhance the performance of the coolant. It helps to lower the freezing point of the mixture, prevent corrosion, and is compatible with other antifreeze components.