Diwan-i Kohi was the department of________ introduced by Muhammad Bin Tughlaq.

The correct answer is agriculture.

Explanation & Context:
1. Diwan-i-Kohi (Diwan-i-Amir-Kohi): Sultan Muhammad bin Tughlaq established a separate department for the development of agriculture named Diwan-i-Kohi.
2. Main Objective: The primary aim of this department was to bring uncultivated land under farming, enhance crop yields, and modernize agricultural practices across the Delhi Sultanate.
3. Financial Support: Through this department, the government provided financial aid and crop loans (known as taccavi or sondhar) directly to peasants to purchase seeds, cattle, and digging tools.