Final answer:
The worst case time efficiency in adding an element in an unsorted array based dictionary is O(n), where n is the number of elements in the array.
Step-by-step explanation:
The worst case time efficiency in adding an element in an unsorted array based dictionary would be O(n), where n is the number of elements in the array. This is because in an unsorted array, you would need to search through the entire array to find the correct position to insert the new element. In the worst case, this would require checking each element until you reach the end of the array.