Mansa musa, the monarch of 14th century mali, is most remembered for a) defending his african kingdom from slave traders. b) his conversion to islam and his pilgrimage to mecca. c) his expansion of the gold trade into central and southern africa. d) lending his massive military forces to the arabs during the crusades.

B) his conversion to Islam and his pilgrimage to Mecca

Explanation:

Mana Moosa was the tenth Mansa and is known as the richest person ever lived. He is famous in the middle ages and Europe as the richest man in history, he went to Hajj in 1337.  

Mansa was the fourteenth emperor. He became rich due to the gold and salt trade that was abundance in West Africa at that time and spent the money to strengthen the culture of Timbaktu.

The Djinguerber Mosque and Snkore University was established during his rule. He went to the Mecca in 17th year of his reign. Although the founder of the empire were not Muslims but later the kings adopted Islam and it was declared  the state religion  by Mansa Moosa, he went to pilgrimage in 1324. His Hajj was important because he he was the first west African emperor to go to Hajj.