Final answer:
The slowest operation on an ArrayList with 10,000 items is adding an item at the beginning of the list because it requires shifting all subsequent elements, making it a time-consuming O(n) operation.
Step-by-step explanation:
The student's question pertains to the performance of different operations on an ArrayList in Java containing 10,000 items. Among the given options, the operation that is performed the slowest is C. productList.add(0, item). This is because inserting an item at the beginning of the list requires all subsequent elements in the list to be shifted one position to the right to accommodate the new element, which is a time-consuming operation with a time complexity of O(n). In contrast, productList.set(0, item) is a quick operation because it simply replaces the element at the specified index without shifting elements, which has a time complexity of O(1). Similarly, productList.add(item) is typically fast as it adds the element to the end of the list, but can occasionally be slower if the list needs to resize. Lastly, productList.remove(index) could vary in speed depending on the index, but removing an element also involves shifting elements to fill the gap left by the removed element.