Final answer:
Isabella and Ferdinand expelled Jews and Muslims from Spain as part of a campaign for political unification under the Catholic religion, making answer option a) Political unification correct.
Step-by-step explanation:
The reason behind Isabella and Ferdinand expelling Jews and Muslims from Spain was to achieve political unification under the Catholic faith. Religious tolerance had been a characteristic of the region, especially during the period of Al-Andalus where Christians, Jews, and Muslims coexisted. The Inquisition established rigid adherence to Catholicism, and the Reconquista marked the effort to drive Islam out of the Iberian Peninsula. The expulsion of Jews and Muslims can be seen as a part of this broader campaign to consolidate Catholic power and create a religiously uniform nation, thus the correct answer is a) Political unification. This also falls in line with the wider European Age of Exploration motives, such as the desire to spread Christianity.