Explanation

Sodium, potassium and rubidium are highly reactive alkali metals that ignite in air and react violently with water, so they are stored under kerosene or mineral oil to isolate them. Lithium is the exception: it is less dense than mineral oil and would float to the surface, exposing it to air. It is therefore stored in an inert atmosphere or sealed in paraffin wax rather than under oil. Hence option D is correct.