There is direct contact made between the corn and the butter. Thus, heat is transferred by conduction.
Through conduction; conduction=contact, radiation=electromagnetic waves, convection=movement in liquids and gasses.
The butter melted when it came into contact with the corn because heat was transferred from the corn to the butter by conduction, which is the direct transfer of heat through contact between two objects. This process involves heat moving from a warmer object (the corn) to a cooler one (the butter).
;