Final answer:
Alex exhibits the 'duty of obedience' by dutifully following his client's request to place a box of booties by the front door, which is a lawful and harmless instruction.
Step-by-step explanation:
The fiduciary duty demonstrated by Alex in this scenario is the duty of obedience. As an agent for his client, Alex is required to follow lawful instructions, requests, and directives given by his client, as long as they do not cause harm or violate any legal or ethical standards. In the context provided, placing a box of booties by the front door with a sign for visitors follows his client's request without leading to any harm; thus, he fulfills the duty of obedience to his client's wishes regarding the care and condition of the home during viewings.