Question 40 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is C ### Why Option C is Correct: Ethylene glycol (often referred to simply as "antifreeze") is mixed with water in engine cooling systems to improve the operational range of the coolant. This occurs through two distinct chemical phenomena: 1. **Freezing Point Depression:** The presence of ethylene glycol molecules disrupts the formation of the regular crystalline structure of water (ice). This requires a much lower temperature for the mixture to freeze compared to pure water, preventing catastrophic engine damage (like cracked blocks or heads) in cold weather. 2. **Boiling Point Elevation:** The ethylene glycol molecules increase the intermolecular forces required for the mixture to vaporize. This raises the boiling point of the coolant above that of pure water, allowing the engine to operate at higher temperatures without the coolant turning to steam, thereby improving heat transfer efficiency and preventing overheating. Therefore, the primary function of the ethylene glycol mixture is **Freezing point depression and boiling point elevation.** ### Why Other Options Are Incorrect: * **A) Freezing point and boiling point elevation:** This is incorrect. While the boiling point is elevated (raised), the freezing point is depressed (lowered). Raising the freezing point would make the coolant freeze at warmer temperatures, defeating the purpose of antifreeze. * **B) Freezing point and boiling point depression:** This is incorrect. While the freezing point is depressed (lowered), the boiling point is elevated (raised). Lowering the boiling point would cause the engine to overheat and boil the coolant much more easily. * **D) Freezing point elevation and boiling point depression:** This is incorrect. This combination of effects (raising the freezing point and lowering the boiling point) would make the cooling system useless for engine operation, causing freezing in cold weather and boiling in normal operation.