Final answer:
The boiling point of water at 672 mm Hg will be lower than 100°C, and given the provided options, the closest estimate is 80°C, which is answer option (b).
Step-by-step explanation:
The boiling point of water changes with atmospheric pressure and since standard atmospheric pressure is defined as 760 mm Hg, water boils at 100°C at this pressure. When the atmospheric pressure is lower than 760 mm Hg, water boils at a lower temperature. The question asks for the boiling temperature of water at 672 mm Hg, which is less than the standard atmospheric pressure.
Therefore, the boiling point of water at 672 mm Hg would be lower than 100°C. Boiling points are affected by external pressure; in particular, water's boiling point is lower at pressures below 760 mm Hg. Although the exact temperature is not provided, we can deduce that the boiling point will be somewhere between 80°C and 100°C, but not as low as 60°C or 40°C. Considering available options and without exact calculations or data, the closest estimate would be option (b) 80°C, but please note that this is an approximation. For a precise determination, a vapor pressure curve for water would be needed.