Lesson 4.3.5.2

4.3.5.2 Merge sort Quiz: AQA Computer Science, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.3.5.2, Merge sort: 20 multiple choice questions for the AQA Computer Science (7517), Unit 3: Fundamentals of algorithms, written with Revision Ninja.

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The 20 questions

  1. What is the time complexity of merge sort?

    • O(n log n)
    • O(log n)
    • O(n log n squared)
    • O(n^2)

  2. Merge sort is an example of which approach to problem solving?

    • Dynamic programming only
    • Greedy
    • Brute force
    • Divide and conquer

  3. What does merge sort do first with a list?

    • Scans the list for duplicate values
    • Divides the list into smaller halves until each part holds a single item
    • Creates a binary tree of comparisons between every pair of items in the list
    • Finds the largest item

  4. In the merge step of merge sort, what happens?

    • Items are swapped until the list is reversed
    • Two lists are joined end to end without comparison
    • The largest item is removed from each list
    • Two sorted lists are combined by repeatedly taking the smaller front item

  5. Why is merge sort O(n log n) while bubble sort is O(n^2)?

    • Merge sort compares each item only once overall, so it runs in linear time for every list
    • Merge sort never swaps items
    • Merge sort halves the list about log n times, and each level of merging costs O(n)
    • Merge sort uses a fixed number of passes

  6. What extra storage does merge sort typically need during merging?

    • Auxiliary space proportional to n
    • No extra storage
    • A single constant variable
    • Space proportional to n squared

  7. Merge two sorted lists [1, 4, 7] and [2, 3, 8]. What is the result?

    • [1, 2, 3, 4, 8, 7]
    • [1, 2, 3, 4, 7, 8]
    • [2, 3, 1, 4, 7, 8]
    • [1, 4, 7, 2, 3, 8]

  8. How many times can an 8-item list be halved before single items remain?

    • 8
    • 4
    • 2
    • 3

  9. What is the sorted output of merge sort applied to [38, 27, 43, 3]?

    • [3, 38, 27, 43]
    • [38, 27, 3, 43]
    • [27, 3, 38, 43]
    • [3, 27, 38, 43]

  10. Merging the sorted lists [2, 6, 9] and [1, 5] with the standard merge step, what is the first item output?

    • 2
    • 1
    • 9
    • 5

  11. What is the maximum number of comparisons needed to merge two sorted lists of lengths 4 and 4?

    • 8
    • 16
    • 4
    • 7

  12. How many halving levels does merge sort use for 1024 items?

    • 1024
    • 512
    • 10
    • 5

  13. Roughly how many operations does merge sort need for n = 1024 items?

    • 1048576
    • 10240
    • 1024
    • 523776

  14. Compared with bubble sort on the same 1024 items, merge sort needs roughly how many times fewer operations?

    • About 2 times
    • About 10 times
    • About 50 times
    • About 1000 times

  15. Why is the merge step stable when ties are resolved in favour of the left list?

    • The sort becomes O(n^2)
    • Equal items keep their original relative order
    • Equal items are removed from the result
    • Items are reversed during the merge

  16. What is the recursion depth of merge sort on n items?

    • n levels
    • Exactly two levels
    • n squared levels
    • About log2 n levels

  17. Roughly how many comparisons does merge sort need to sort 1000 items?

    • About 1,000,000
    • About 1,000
    • About 10,000
    • About 100,000

  18. Which is a valid reason to prefer merge sort over bubble sort for large data sets?

    • Merge sort never needs any comparisons
    • Bubble sort cannot run on modern computers
    • Merge sort uses less memory than any algorithm
    • Its O(n log n) growth keeps running time manageable as n increases

  19. A merge sort sorts 16 items. How many merge operations occur in total?

    • 16
    • 8
    • 15
    • 4

  20. What is the running time of merge sort on a list that is already sorted?

    • O(1)
    • O(n^2)
    • O(n), because it stops early
    • O(n log n), because it still divides and merges

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