Question

how can water be boiled and zero degree celsius

Answer 1

There is a way to boil water at 0°C, there are two main factors which determine the boiling of water. It includes high temperature and pressure. So if you are able to increase the pressure and make it equal to the Vapour pressure then the water can easily boil at 0°C. The pressure of air above the column of water my must be atleast or approximately 611.73 Pa. This can make the water boil even in a freezing temperature.