Step 1: Understand what the question is asking.
We need to identify the specific management process through which a manager synchronizes or unifies the activities of different departments.
Step 2: Define Management.
Management is the broad, overall process of planning, organising, directing, and controlling the activities of an organisation. It is not specific to synchronization.
Step 3: Define Planning.
Planning involves setting objectives and deciding the best course of action to achieve them in advance. It does not focus on synchronizing departments.
Step 4: Define Organising.
Organising involves structuring people, resources, and tasks into a working framework. It creates the structure but does not synchronize ongoing activities between departments.
Step 5: Define Co-ordination.
Co-ordination is the process of synchronizing, integrating, and unifying the efforts of various individuals and departments so that all of them move in the same direction to achieve common organisational goals. It is often called the essence of management.
Step 6: Match the definition to the question.
The question says a manager synchronizes activities of different departments. This is precisely what Co-ordination means.
\[ \boxed{ \text{(D) Co-ordination} } \]