According to the PMBOK® Guide, specifically in the section describing the Project Manager ' s Role, there is a fundamental distinction between Integration Management and all other Knowledge Areas.

The Responsibility of Integration: Project Integration Management is the core of the project manager’s role. It involves coordinating all other knowledge areas, making trade-offs among competing objectives, and managing the interdependencies among the project management processes.

Why it Cannot be Delegated: While a project manager may delegate specific tasks to specialists—such as a Scheduler for Schedule Management, a Cost Estimator for Cost Management, or a Risk Officer for Risk Management—the responsibility for Integration belongs solely to the project manager. Only the project manager has the " big picture " view necessary to combine the results from all other areas into a cohesive whole and ensure the project remains aligned with the Project Charter and organizational objectives.

Analysis of other options:

Project Cost Management (Option A): In large organizations, this is often handled or heavily supported by financial analysts, accountants, or cost engineers.

Project Risk Management (Option C): On large, complex projects, a dedicated Risk Manager or a risk specialist may be appointed to lead the identification and analysis of project risks.

Project Schedule Management (Option D): It is very common for a project manager to delegate the detailed creation and maintenance of the project schedule to a professional Scheduler or a Project Management Office (PMO) specialist.

Per PMI standards, the project manager is the integrator. They are the only person responsible for the project as a whole, meaning they must be the ones to lead the integration of the various pieces of work into a unified project management plan.