Why is sodium kept immersed in kerosene oil?

Explanation

Sodium reacts both with air and water. It is a highly reactive metal. When kept in open, it readily combines with oxygen present in air to form its oxide. Similarly, it reacts with water or moisture to form sodium hydroxide.
`4Na_((s)) + O_(2(g)) to 2Na_(2)O_((g))`
`2Na_((s)) + underset((Moisture"))(2H_(2)O_(l)) to 2NaOH_((aq)) + H_(2(g))`
in order to preserve sodium metal, we generally keep it under kerosene so that neither air nor moisture may come in its contact.