Sodium reacts with air and water both. 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 vapours or moisture to form sodium hydroxide.
`4Na(s) + O_(2)(g) rarr 2Na_(2)O(s)`
`2Na(s) + underset(("Moisture"))(2H_(2)O(l)) rarr 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.
