Final answer:
The example of real estate is Alex's purchase of a house, as it involves acquiring the physical property, both the structure and the land associated with it.
Step-by-step explanation:
Based on the definitions of "real estate" and "real property" provided, the example that represents real estate is Alex has bought a house for his extended family. Real estate refers to the physical property itself, which can include structures and land. In this case, Alex's purchase of a house, which is a structure and likely includes a parcel of land, directly corresponds to the definition of real estate. Grating an easement or selling air rights are rights associated with the property but do not represent the physical property itself. Leasing a horse ranch is a temporary arrangement and does not constitute ownership of real estate.