* Solid (ice): If the temperature is exactly 0 degrees Celsius and the water is at or below its freezing point, it will be in the solid state as ice.

* Liquid (water): If the temperature is exactly 0 degrees Celsius and the water is at or above its freezing point, it will be in the liquid state as water.

This is because 0 degrees Celsius is the freezing point of water, meaning it's the temperature at which water can transition between solid and liquid states. The specific state depends on whether the water is gaining or losing heat at that moment.