it should be O(log n) because
min element will be root takes O(1).
2nd smallest will be at level 1(root is level 0)
3rd smallest element will be at 2nd or 3rd level
similarly 7th smallest element can be found in level 1 to level 6
now we can not do traversal in min-heap or max-heap so first have to delete smallest element then only 2nd smallest element can be found.
after each deletion we have to perform heapify operation which takes O(logn)
so for doing k operation we will require O(k*log n)=O(log n)