for conduction to occur particles must be:
large,

small,

in contact,

spread apart.

in contact

Explanation:

Conduction is one of the three methods of transfer of heat. In conduction, heat is transferred through the collisions of the particles of two different objects: the particles of the hotter object move faster (on average) than the particles of the colder object, so when they collide with the particles of the colder object, they give part of their kinetic energy. As a result, the average kinetic energy of the particles of the colder object increase, so this object gets warmer.

Based on the description of this phenomenon, it becomes clear that conduction cannot occur if there is no contact between the particles.