The main economic motive of opening the Suez canal was :

To reduce the cost of transportation

The main economic motive of opening the Suez Canal was to reduce the cost of transportation.

Before the Suez Canal was built, ships traveling between Europe and Asia had to sail around the Cape of Good Hope, which is the southernmost tip of Africa. This was a long and dangerous journey, and it also made shipping expensive. The Suez Canal, which cuts through the Isthmus of Suez, provides a much shorter and more direct route between Europe and Asia. This significantly reduced the cost of transportation and made it possible to trade more goods between these two continents.

The other options are not the main economic motives of opening the Suez Canal. Maintaining political relations with Europe, developing cultural relations with Egypt, and developing the navigation system were all secondary benefits of the canal. However, the primary goal was to reduce the cost of transportation.