Explanation:

- Option 1: Nazir

- The Nazir was often responsible for overseeing administrative tasks such as revenue collection and managing state expenses, not specifically related to maintaining merchant registers.

- Option 2: Rais Parwana

- This position is not typically associated with the economic administration or maintaining records of merchants. Its responsibilities are often related to higher authority approvals and official documentation.

- Option 3: Muhtasib

- The Muhtasib was an officer responsible for ensuring public morality and adherence to Islamic laws, monitoring market prices for fairness but not specifically for maintaining merchant registers.

- Option 4: Shahna-i-Mandi

- The Shahna-i-Mandi was specifically tasked with overseeing market operations, including maintaining a register of merchants to ensure an adequate supply of goods. This role was crucial for economic regulation during Alauddin Khilji's reign.

- Answer: Shahna-i-Mandi