If a material conducts heat easily, it is a good

Your answer would be conductor.

It would be thermal conductor

Explanation:

Thermal conductivity is attributed to the exchange of energy between adjacent molecules and electrons in the conducting medium. A substance of large thermal conductivity k is a good heat conductor, whereas one with small thermal conductivity is a poor heat conductor or good thermal insulator.

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.