Question

At very low pressure what is the boiling point and freezing point of water?
A. $0.01^\circ {\text{C}}$
B. $0.02^\circ {\text{C}}$
C. $0.05^\circ {\text{C}}$
D. $0.03^\circ {\text{C}}$

Answer 1

Here we have to apply the concept of the triple point of water.
The three water states, which are called triple water points, will co-exist at extremely low pressure and a certain temperature.

Complete step by step answer: Triple point of water- The temperature and pressure at which in the liquid, solid and gaseous states a substance can exist in equilibrium.
It is important to remember that the triple water point coincides with the pressure required for the presence of liquid water. Since ice is less dense than liquid water, it is immediately sublimated into water vapour by ice freezing at pressures below three stages.
For water the triple point temperature is $0.01^\circ {\text{C}}$ i.e. water can freeze and boil at this temperature. It is the freezing and boiling point of water.
Hence, from the above discussion we can conclude that option A is the correct answer.
At very low pressure what is the boiling point and freezing point of water is $0.01^\circ {\text{C}}$ .

Additional information:
The melting and freezing point describe the same transformation of matter, in this case from liquid to solid or equivalently from solid to liquid. The boiling and freezing point are the same at triple point because here the whole melting and freezing point is struck on $0.01^\circ {\text{C}}$ during the triple point process.

Note: The key difference between the boiling and the melting point is that the temperature at which solid and liquid phases are in equilibrium is known as the melting point, while the boiling point is the temperature at which a liquid’s vapour pressure equals the external pressure.