Water present in the system can freeze if

• A. A large amount of coolant is added
• B. A small vacuum pump is used
• C. A large vacuum pump is used for evacuation
• D. The system is warmed to room temperature

Answer: (C)

Leading idea: when pressure around water drops enough, it begins to boil at that temperature, and the energy required for boiling comes from the water itself, causing rapid cooling that can drive the water below freezing.

Using a large vacuum pump for evacuation lowers the surrounding pressure very quickly and drastically. As the water starts to boil, latent heat is drawn from the water, cooling it rapidly. If the heat input isn’t enough to compensate, the water can drop below 0°C and freeze. The other options don’t drive this cooling effect: adding coolant lowers the temperature and helps prevent freezing, a small vacuum pump won’t achieve the strong pressure drop needed for significant evaporative cooling, and warming to room temperature raises temperature rather than causing freezing.