What act involves a real estate professional acting on behalf of a client in transactions?

The correct answer is Agency. Agency is a legal concept in real estate that establishes a relationship between a real estate professional, known as the agent, and a client, referred to as the principal. In this relationship, the agent is authorized to act on behalf of the client in various transactions, which can involve buying, selling, leasing, or managing property. The essence of agency is that the agent has a fiduciary duty to act in the best interests of the principal, which includes providing relevant information, negotiating terms, and representing the client's interests throughout the process.

This relationship is foundational in the real estate industry and allows clients to rely on the expertise and skills of their agents, ensuring that their needs are effectively represented. This is distinct from other concepts like representation, which can be broader and does not necessarily imply a formalized agency relationship, and delegation or mandate, which pertain to different aspects of authority and responsibility.