What business analysis plan defines the process to be followed in managing the solution scope and requirements?

The requirements management plan establishes the activities, tools, and governance processes the business analyst team will follow to manage the full requirements lifecycle, including how requirements are identified, prioritized, changed, and approved. It is a dedicated business analysis plan - not a general project document - that provides the framework for managing solution scope and all associated requirements.

The scope management plan is a project management artifact focused on defining and controlling the overall project scope, not specifically on the processes for managing solution requirements.

The change management plan addresses how organizational changes will be communicated and adopted by people, not how requirements will be tracked and governed.

The project management plan is a high-level umbrella document covering all aspects of project delivery - it may reference a requirements management plan as a subsidiary, but is itself not a business analysis planning document.