Which operation involves replacing a unit in an area while transferring mission responsibilities?

Relief in place is the correct choice because it specifically describes an operational procedure where one unit is replaced by another in a designated area while transferring mission responsibilities. This operation is often executed to ensure continuity of command and operations, allowing the incoming unit to take over tasks without interrupting the flow of the mission.

In the context of military operations, this process is vital for maintaining operational effectiveness and can involve elements such as intelligence sharing, logistical support, and coordination to ensure a seamless transition.

The other options, while relevant within military operations, do not define the process of unit replacement in the same manner. For instance, interdict refers to disrupting the enemy's ability to move or operate, neutralize typically means to render a threat ineffective, and occupy does not imply the transfer of responsibilities but rather establishing control over an area.