What is the type of bonding between sodium and potassium?
No bonding exists between the two, as both are metals. However, it can be said that metallic bonding exists naturally within potassium and sodium respectively. For ionic bonding, a metal must be bonded with a non-metal. For covalent bonding, a metal is bonded with a non-metal (usually) metallic bonding exists in a metal per se, and it does not require any bonding with any other element.