Why is sodium stored under kerosene or in a nitrogen atmosphere?

Sodium is a highly reactive metal that reacts readily with air and moisture. When exposed to ordinary air, it forms a film of sodium hydroxide, which subsequently absorbs carbon dioxide to create sodium bicarbonate.1

Because sodium is so reactive with oxygen and water vapor, it must be stored in environments that prevent these reactions. It is typically kept immersed in inert liquids, such as kerosene or naphtha, or stored under a nitrogen atmosphere, as sodium does not react with nitrogen. Proper storage is essential for safety, as sodium can ignite in air—particularly in liquid form—and its reaction with water is highly exothermic, posing significant explosive hazards due to the release of hydrogen gas.1