Final answer:
The chemistry teacher is investigating the boiling point of bromine, which is a physical property influenced by intermolecular forces.
Step-by-step explanation:
The chemistry teacher investigating the boiling point of bromine is studying a physical property of bromine. The correct answer to which property is being investigated is c. Boiling point. The boiling point of a substance is influenced by intermolecular forces, as well as by the presence of solutes in a solution, which impacts the colligative properties. Substances with similar molar masses can have different boiling points due to these intermolecular forces. Determining boiling points is essential for identifying substances, studying their properties, and understanding their behavior under different conditions.