Option D Bubble Sort
Time complexity of merge sort is $O(nlogn)$ in all cases best ,average, worst
time complexity of quick sort in best case $O(nlogn)$ and in worst case $O(n^{2})$
time complexity of sell sort in best case $O(nlogn)$ and in worst case $O(n^{2})$
Time complexity of Bubble sort take $O(n^{2})$ in all case best ,average ,and worst so bubble sort is slowest in among all.