Which agreement involves a principal and a broker to buy, sell, lease, or manage a property?

The correct choice is the agency contract because it specifically establishes a legal relationship between a principal and an agent, typically a broker in real estate. This type of agreement empowers the broker to act on behalf of the principal in transactions involving buying, selling, leasing, or managing property. The agency contract outlines the rights and obligations of both parties and is fundamental in agency law, as it formalizes the authority granted to the broker to represent the principal's interests in real estate transactions.

The other options do not accurately describe this relationship. An employment contract typically refers to the terms and conditions of employment between an employer and employee, which does not encompass the same agency relationship. A service agreement may involve the provision of services but lacks the specific legal framework that defines the agency relationship. A business contract is a broad term that can encompass many types of agreements but does not specifically refer to the delegation of authority that occurs within an agency contract.