Final answer:
The boiling point of water increases with pressure. At 4 Mpa, the temperature at which water boils is significantly higher than the standard boiling point at 1 atm. The closest correct answer is 250.4°C.
Step-by-step explanation:
The question asks about the boiling point of water at a specific pressure. The boiling point of water varies with pressure; at a pressure of 1 atm (101.3 kPa), the boiling point is the standard 100°C. However, when the pressure is increased to 4 Mpa (or 4000 kPa, which is significantly higher than 1 atm), the boiling point also increases since the vapor pressure needs to be greater to allow water molecules to escape into the gas phase.
From the provided reference information, we can deduce that the boiling point of water at a pressure greater than 1 atm is higher than 100°C. The vapor pressure curve intersects at about 110°C at a pressure of 1000 mmHg (approximately 133.322 kPa). Since 4 Mpa is much higher than this pressure, the boiling point at 4 Mpa would be considerably higher than 110°C. Therefore, given the options, the closest correct answer to the temperature at which water boils at a pressure of 4 Mpa is (a) 250.4°C.