Sodium metal is kept under

Sodium is a highly reactive alkali metal that reacts vigorously with air (oxygen and moisture) and can explode in contact with water. To prevent this reaction, sodium metal is stored under kerosene oil, which creates an inert environment by preventing contact with air and moisture. Kerosene does not react with sodium and provides a protective layer. Water, alcohol, and petrol are all unsuitable - water and alcohol would react dangerously with sodium, while petrol is too volatile.