The Vadakkumkur and Thekkumkur kingdoms were rivals owing allegiance to:

The correct answer is: C) Zamorin’s Kozhikode.

The Vadakkumkur and Thekkumkur kingdoms were rivals owing allegiance to the Zamorin of Kozhikode. The Zamorin was the ruler of the Kingdom of Kozhikode, one of the most powerful kingdoms in Kerala during the Middle Ages. The Vadakkumkur and Thekkumkur kingdoms were located in the northern part of Kerala, and they were often at war with each other. The Zamorin would often intervene in these wars, supporting one kingdom against the other. This rivalry between the Vadakkumkur and Thekkumkur kingdoms continued for centuries, and it was only in the 18th century that they were finally united under the rule of the Travancore kingdom.

The other options are incorrect because:

• Option A is incorrect because Travancore was a rival of the Zamorin’s Kozhikode.
• Option B is incorrect because Cochin was a vassal state of the Zamorin’s Kozhikode.
• Option D is incorrect because Kolathunadu was a rival of the Zamorin’s Kozhikode.