What happens to water 100°C as pressure is increased from 0.7 atm to 1.4 atm

Explanation:

The graph shows the phase diagram of water . From it , it is clear that at 100°C water remains in equilibrium with water vapour and at this temperature , the vapour pressure is equal to one  atm . So this must be boiling point of water.

At 0.7 atm pressure , boiling point must have been reduced . So when water is at 100°C , it must have been completely in vapour phase .

Now the pressure is increased to 1.4 atm . In this process of increase of pressure , the water in vapour state must have turned into liquid state as soon as the pressure increases beyond  1 atm . Beyond it its boiling point would have increased above  100°C so it can not remain in gaseous phase . At 1.4 atm , its boiling point would have increased to 110°C or so . Hence it must be in liquid phase because its temperature is below its boiling point at that pressure .

Hence water changes from gaseous phase to liquid phase when pressure changes from 0.7atm to 1.4 atm .

the answer to this question is 3.