Option b is the correct answer. The first Sultan of Delhi to introduce regular coins and declare Delhi as the capital of his empire was Iltutmish. Iltutmish introduced the silver tanka and the copper jital coins. His new bimetallic coinage system addressed the silver shortage issue and became the foundation for coinage during the Sultanate period. He also moved the capital to Delhi from Lahore after dethroning his predecessor Aram Shah in 1211. Iltutmish shifted the capital to Delhi due to its strategic location, central to his expanding empire. This relocation facilitated better administration and defense, solidifying his rule and contributing to the growth of the Delhi Sultanate.