Final answer:
Sodium (Na) is likely to have the highest thermal conductivity of the elements listed because it is an alkali metal, and metals on the left side of the periodic table generally exhibit high thermal conductivity.
Step-by-step explanation:
When looking at thermal conductivity, metals generally have higher thermal conductivity than non-metals due to the ability of free electrons to transport energy. Among the options provided (Antimony, Carbon, Sodium, and Gallium), Sodium (Na) is expected to have the highest thermal conductivity. This is because Sodium is an alkali metal, and metals on the left side of the periodic table typically have higher thermal conductivities compared to other elements. Even though carbon in the form of diamond has extremely high thermal conductivity, it is an exception to the rule, and the form of carbon mentioned in the question, likely graphite, is not specified to be this high conductivity form. Therefore, for the elements listed, Sodium would be the most likely to have the highest thermal conductivity.