Answer : 2. "गागरोन दुर्ग"
Explanation :

Water (Udak) Fort:- The fort or fort which is surrounded by water on all sides is called water fort. Example:- Gagron, Manoharthana (Jhalawar), Bhainsrodgarh (Chittorgarh), Shergarh. Most of the forts in Rajasthan fall in this category.