Heated water under pressure is converted into vapor by what method?

Heated water under pressure is converted into vapor primarily by decreasing its pressure. This process utilizes the principle that a liquid will boil and turn into vapor when its pressure is reduced to a level where its vapor pressure exceeds the surrounding pressure. By lowering the pressure, the boiling point of the water decreases, allowing it to transition to the vapor phase at a lower temperature.

In contrast, simply heating water (the first option) raises its temperature but does not necessarily lead to vaporization unless the pressure is also appropriate. Cooling (the third option) would further reduce the temperature of the water, making vaporization less likely as it would move towards the liquid state. The fourth option, pressurizing further, would increase the pressure on the water, which generally raises the boiling point, thus preventing it from converting to vapor until the pressure is relieved.

Therefore, adjusting the pressure downwards is the most effective method for converting heated water to vapor in a controlled manner.