Final answer:
The groove for the tendon of the flexor hallucis longus muscle is located on the medial side of the distal end of the tibia, known as the medial malleolus.
Step-by-step explanation:
The groove for the tendon of the flexor hallucis longus muscle is located on the medial side of the distal end of the tibia, known as the medial malleolus. The medial malleolus forms a bony bump on the inner side of the ankle region and articulates with the talus bone of the foot. So, the correct answer is 2) Medial malleolus.