Correct Option (C):
Nasir-ud-din Mahmud (1394–1412 CE) was the last ruler of the Tughlaq dynasty. His reign was characterized by severe internal fragmentation and the devastating invasion of Timur in 1398 CE, which resulted in the sacking of Delhi and further weakened the Sultanate. The Tughlaq dynasty effectively ended with his demise in 1412 CE, paving the way for the establishment of the Sayyid dynasty.
Incorrect Options:
Firoz Shah Tughlaq: He ruled from 1351 to 1388 CE. While his reign is noted for administrative reforms and public works, he was not the last ruler of the dynasty. The decline of the Tughlaq dynasty commenced after his death.
Ghiyas-ud-din Tughlaq Shah II: He succeeded Firoz Shah Tughlaq and had a very brief reign from 1388 to 1389 CE. He was one of the immediate successors during the period of dynastic instability but not the final ruler.
Nasrat Shah: He was a rival claimant to the Tughlaq throne during the period of dynastic decline, ruling concurrently from Firozabad while Nasir-ud-din Mahmud held Delhi. He was not the last undisputed ruler of the Tughlaq dynasty.