The correct answer is option 2, Lothal. The site of Lothal, located in present-day Gujarat, India, was a prominent city of the Indus Valley Civilization. One of the unique features of Lothal was its ancient dockyard, making it a significant trade and commerce hub of the civilization.

Option 1, Kalibangan, is incorrect. Kalibangan was also an important city of the Indus Valley Civilization, but it did not have an ancient dockyard.

Option 3, Rangpur, is incorrect. Rangpur is not associated with the Indus Valley Civilization, so it could not have had an ancient dockyard.

Option 4, Harappa, is incorrect. Harappa was one of the major cities of the Indus Valley Civilization, but it did not have an ancient dockyard. However, Harappa was known for its impressive urban planning and architecture.

Therefore, the correct answer is option 2, Lothal, as it was the site of the Indus Valley Civilization that had an ancient dockyard.