Step-by-step Solution:

1. (a) To find the lower/upper bound in an ordered sequence: Binary search can effectively determine the lower or upper bounds of elements within a sorted ordered sequence.\[\] 2. (b) Union of intervals: Union of intervals typically involves interval merging algorithms and is not solved using binary search.\[\] 3. (c) Debugging: Debugging sometimes uses binary search in software engineering to isolate the part of the code where a problem is introduced. This is a form of "binary search" to find errors.\[\] 4. (d) To search in unordered list: Binary search only works on sorted arrays or sequences. Searching in an unordered list is not feasible using binary search directly because binary search relies on sorted order comparisons.\[\] \[\] Correct Answer: (d)