Lesson 4.5.6.9

4.5.6.9 Data compression Quiz: AQA Computer Science, Unit 5

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.5.6.9, Data compression: 20 multiple choice questions for the AQA Computer Science (7517), Unit 5: Fundamentals of data representation, written with Revision Ninja.

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The 20 questions

  1. What is the primary purpose of compressing image and audio files?

    • Encrypt data securely
    • Improve image quality
    • Increase sound volume
    • Reduce file size

  2. Which compression type is typically suitable for text files?

    • Lossy compression
    • Sampled compression
    • Lossless compression
    • Frequency truncation

  3. What is the defining feature of lossless data compression?

    • Fixed output size
    • Permanent data loss
    • Higher storage needs
    • Exact data recovery

  4. What occurs during lossy compression of a media file?

    • Original is preserved
    • Data is discarded
    • Data is duplicated
    • File size increases

  5. What does RLE stand for in compression?

    • Reduced length expansion
    • Repeated list enumeration
    • Random lookup encoding
    • Run length encoding

  6. Which compression technique replaces repeated character strings with references in a table?

    • Lossy compression
    • Transform coding
    • Run length encoding
    • Dictionary encoding

  7. Which image file format uses a lossy compression method?

    • JPEG
    • PNG
    • TIFF
    • BMP

  8. Encode the string AAAABBBCCD using run length encoding as count and letter pairs. What is the result?

    • 4A3B2C2D
    • A4B3C2D1
    • 10A3B2C1D
    • 4A3B2C1D

  9. Decode the run length encoded string 3X2Y4Z. What is the original?

    • XYXYXYZZZZ
    • XXXYYZZZ
    • XXXYYYZZZZ
    • XXXYYZZZZ

  10. A run of 50 identical pixels is stored as one count byte and one value byte. How many bytes does the run take?

    • 50 bytes
    • 25 bytes
    • 100 bytes
    • 2 bytes

  11. What happens when run length encoding is used on data without repeating patterns?

    • File size increases
    • File size halves
    • Data is lost
    • Processing halts

  12. What is the compression ratio if a 1000-byte file is reduced to 400 bytes?

    • 0.4 to 1
    • 4 to 1
    • 2.5 to 1
    • 2 to 1

  13. Can an image compressed with a lossy algorithm be restored to its exact original form?

    • Only with password
    • Yes
    • No
    • Only if encrypted

  14. Which type of data compresses most effectively using run-length encoding (RLE)?

    • High-frequency audio
    • Unique text characters
    • Long repeated sequences
    • Random noise data

  15. Why are dictionary-based compression techniques particularly effective for English text?

    • Random character strings
    • Unique vocabulary
    • Repeated words
    • Fixed word lengths

  16. Why does lossy compression achieve significantly smaller file sizes than lossless compression?

    • Duplicates common bytes
    • Encrypts file headers
    • Restores original data
    • Discards redundant detail

  17. What must a decoder use to successfully decompress dictionary-compressed text?

    • The original file
    • A Huffman tree
    • The same dictionary
    • An encryption key

  18. What happens to original audio data after lossless compression and decompression?

    • Quality is reduced
    • Detail is lost
    • Pitch is altered
    • It is identical

  19. Why does repeatedly saving a file using lossy compression continually degrade quality?

    • Accumulated data loss
    • Header corruption
    • Bit depth doubling
    • Increasing file size

  20. What causes visual blocky artifacts in heavily compressed JPEG images?

    • Incorrect screen resolution
    • Corrupted file headers
    • Discarding block detail
    • Lossless encoding errors

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