In C programming, which statement best describes how the quick sort algorithm sorts an array in ascending order?

Introduction / Context:
Quick sort is a widely used divide and conquer sorting algorithm that is often implemented in C standard libraries and competitive programming solutions. It is known for its good average case performance and its recursive partitioning strategy. Understanding the conceptual steps of quick sort is important for algorithm design questions.

Given Data / Assumptions:

• An array of n elements needs to be sorted in ascending order.
• The implementation uses the classic quick sort approach rather than an optimized hybrid variant.
• We are focusing on the conceptual description, not exact C code details.

Concept / Approach:
Quick sort works by selecting a pivot element from the array and partitioning the remaining elements into two groups: those less than or equal to the pivot and those greater than the pivot. After partitioning, the pivot element is in its final sorted position. The algorithm then recursively applies the same partitioning process to the left and right subarrays. Because it divides the problem into smaller subproblems, quick sort uses the divide and conquer paradigm and typically runs in average time O(n log n).

Step-by-Step Solution:
Step 1: Choose a pivot element. This may be the first element, last element, middle element, or a more sophisticated choice such as median-of-three.Step 2: Reorder the array so that all elements less than or equal to the pivot come before it and all elements greater than the pivot come after it. This is the partition step.Step 3: After partitioning, the pivot is in its final sorted position.Step 4: Recursively apply quick sort to the left subarray (elements before the pivot) and the right subarray (elements after the pivot).Step 5: Combine the results. Because the pivot and subarrays are sorted, the whole array becomes sorted.

Verification / Alternative check:
If you simulate quick sort on a small array such as [9, 3, 7, 1], choosing 7 as a pivot, the array is partitioned into [3, 1] and [9] around 7. After sorting the left side to [1, 3] and combining, you get [1, 3, 7, 9]. This matches the divide and conquer partition description given in option B.

Why Other Options Are Wrong:
Option A is selection sort, which repeatedly selects a minimum element rather than partitioning around a pivot.Option C describes insertion sort, which builds a sorted prefix by insertion and shifting.Option D describes merge sort, which merges sorted subarrays rather than partitioning around a pivot.

Common Pitfalls:
Learners often confuse partition based quick sort with merge based merge sort because both are divide and conquer algorithms. A good memory trick is that quick sort partitions first and merges implicitly, while merge sort divides, sorts, and then explicitly merges sorted halves.

Final Answer:
The correct description is It chooses a pivot element, partitions elements less than the pivot to the left and greater than the pivot to the right, and then recursively sorts the partitions.