Final answer:
The item not commonly traded in the trans-Saharan trade route is D. Nuts. Key commodities in this trade included gold, salt, ivory, copper, and slaves. Nuts are not found in historical records as a principal trade item on this route.
Step-by-step explanation:
The commonly traded items in the trans-Saharan trade route included commodities like gold, salt, ivory, enslaved people, copper, precious stones, and kola nuts, among others. However, the item not mentioned among the commonly traded goods in the trans-Saharan trade routes is D. Nuts, which, in many historical accounts, do not feature as a principal commodity within this particular trade network.
Goods such as gold and salt were crucial to the economy of empires like Mali and Songhai, which collected taxes on these products. Salt was particularly valued as it was used to preserve food and maintain human and animal health, while gold was a prestigious and highly sought-after item.