The correct answer is 230 mmHg.
When liquid water boils at 100°C, the water vapor pressure is 760 mmHg
Hence, when liquid water boils at 50°C, the water vapor pressure is (760/2) mmHg or 230 mm Hg.
As the boiling temperature of water halves so does the vapor pressure of water. This is in accordance to Pressure Law.
According to Pressure law, pressure is directly proportional to the absolute temperature, at constant volume.
