Step 1: Understanding the Rashtrakuta Empire.
The Rashtrakuta Empire was one of the most powerful dynasties in medieval India. It ruled large parts of the Indian subcontinent from the 8th to the 10th century and was known for its strong administration, military strength, and cultural achievements.
Step 2: Accounts of Arab travellers.
During the early medieval period, many Arab merchants and travellers visited India and recorded their observations. These travellers wrote about Indian trade, politics, and the strength of various kingdoms.
Step 3: Statement by Sulaiman.
The Arab traveller
Sulaiman, who visited India in the 9th century, mentioned in his travel accounts that the Rashtrakuta Empire was one of the four greatest empires in the world. His statement highlights the global importance and influence of the Rashtrakuta rulers.
Step 4: Analysis of options.
- (A) Alberuni: Incorrect. Alberuni came to India in the 11th century with Mahmud of Ghazni and wrote the book \textit{Kitab-ul-Hind}.
- (B) Al-Masudi: Incorrect. Although he described India, he did not make this specific statement about the Rashtrakutas.
- (C) Sulaiman: Correct. He described the Rashtrakuta Empire as one of the four greatest empires in the world.
- (D) Nikitin: Incorrect. Nikitin was a Russian traveller who visited India in the 15th century.
Step 5: Conclusion.
Thus, the Arab traveller who praised the Rashtrakuta Empire as one of the four greatest empires of the world was Sulaiman.
Final Answer: Sulaiman.