Analyze time complexity and threading trade-offs

Answer the following conceptual questions.

1) Worst-case time complexity

State the worst-case time complexity (Big-O) for each operation and briefly justify.

1. Remove an element (by value) from a sorted array .
2. Check whether a given key exists in a hash table .
3. Remove the minimum element from a min-heap .
4. Find the i-th element in a sorted array (assume 0-based index) and return its value.

2) Multithreading vs single-threading

Is multithreading always faster than single-threading? Explain why or why not, and give at least one concrete example where multithreading is slower.