Question

give reason: phosphorus is stored in water

Answer 1

It is insoluble in water, but soluble in carbon disulfide. It takes fire spontaneously in air, burning to the pentoxide. White phosphorus should bekept under water, as it is dangerously reactive in air, and it should be handled with forceps, as contact with the skin may cause severe burns.

Answer 2

phosphorous is highly reactive with air that's why it is stored in water. Moreover it is insoluble in water
Thus water is the most suitable substance in which phosphorus is to be stored.