During the reign of Iltutmish, the capital of the sultanate was Delhi. Option 1, Agra, is incorrect as Agra became the capital of the Mughal Empire much later. Option 2, Lahore, is also incorrect as Lahore was not the capital during Iltutmish`s reign. Option 3, Badaun, is also incorrect as Badaun was not a capital city during that time. Therefore, option 4, Delhi, is the correct answer. Delhi served as the capital of the Delhi Sultanate under the rule of Iltutmish. It was strategically located in the northern part of India, making it a central hub for administration and governance. The city of Delhi was an important center for political, cultural, and economic activities during the Sultanate period.