Sodium is so reactive that it has to be kept under a layer of oil. The reason for this is that it will readily react with water and oxygen in the air and produce flames. Sodium
is a very soft metal and can be cut with a knife. If a small
piece is cut and exposed to the air, its shiny surface quickly tarnishes as it reacts with the air.
1.a) How is sodium stored?

b) explain your answer.