Question

thermodynamics
definition\t\t\tcharacteristics
the branch of physics that deals with the relationships between heat and other forms of energy.

Explanation:

The problem is about Thermodynamics, which is a subfield of Physics, and Physics falls under Natural Science. The content is about defining and potentially analyzing characteristics of Thermodynamics, so the relevant subfield from the given list for Natural Science is Physics (since Thermodynamics is a branch of Physics).

Answer:

Natural Science - Physics