Final answer:
The boiling point of an unknown liquid at 58°C under a pressure of 670 mm Hg can be true because boiling points vary with external pressure. Normal boiling point is determined at a standard pressure of 760 mm Hg.
Step-by-step explanation:
When discussing the boiling point of an unknown liquid, it is important to understand that this property depends on the ambient pressure surrounding the liquid. The boiling point is defined as the temperature at which a liquid's vapor pressure is equal to the external pressure. Normal boiling point refers to the boiling point of a liquid at a standard atmospheric pressure of 760 mm Hg (1 atm or 101.3 kPa).
Since the pressure you've provided (670 mm Hg) is different from standard pressure, it's indeed possible that an unknown liquid could have a boiling point of 58°C under these conditions. At lower pressures, liquids boil at lower temperatures, so the statement that the unknown liquid has a boiling point of 58°C at 670 mm Hg can be true based on this context, although without additional information about the specific liquid's properties, we cannot say definitively.