Question

Water is present at 2 states at 0 degree.why

Answer 1

Water is present into state because it is depend on its temperature whether it is higher or lower if it is higher it will be a liquid at zero degree temperature if it is lower it will be a solid at zero degree temperature and we know the liquid form of water is water and the solid form of water is ice
Hope it will help you dear

Answer 2

State changes are kind of weird in that they require energy. If the water is already frozen as ice, then heat added to the ice will cause it to increase in temperature until 0 Celsius. At that point, additional heat added to the system is used as energy for the state change to liquid water. The ice cannot exist at a temperature greater than that, but at the same time the water cannot exist until enough energy has been added to transition the mass of ice into liquid.So if energy of the system is exactly enough to make the temperature of the ice 0 and no more, then no state change will occur.