Which of the following sorting algorithms has the lowest worst-case complexity?

Answer: Merge sort

Reasoning:

• Merge sort — worst-case O(n log n). The algorithm always divides the array and merges sorted halves, guaranteeing O(n log n) time.

• Quick Sort — worst-case O(n^2), average-case O(n log n). The worst-case arises with poor pivot choices (for example, already sorted input without pivot protection).

• Bubble Sort — worst-case O(n^2). Repeated pairwise swaps lead to quadratic time on large inputs.

• Selection Sort — worst-case O(n^2). Selecting the minimum repeatedly results in quadratic time regardless of initial ordering.

Conclusion: Among the listed algorithms, Merge sort has the lowest worst-case time complexity (O(n log n)), while the others can take O(n^2) in the worst case.