Lesson 4.2.5.1

4.2.5.1 Trees and binary trees Quiz: AQA Computer Science, Unit 2

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.2.5.1, Trees and binary trees: 20 multiple choice questions for the AQA Computer Science (7517), Unit 2: Fundamentals of data structures, written with Revision Ninja.

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The 20 questions

  1. What is a tree in graph terms?

    • A directed graph with two cycles
    • A connected, undirected graph with no cycles
    • A graph with no vertices
    • A graph in which every vertex has exactly two edges

  2. What is a rooted tree?

    • A tree with no edges
    • A tree in which one vertex is designated as the root
    • A tree in which every node has exactly three children
    • A tree that contains a cycle

  3. In a rooted tree, which node has no parent?

    • Every node
    • A leaf
    • The root
    • Any internal node

  4. What is a binary tree?

    • A tree in which every node has exactly four children
    • A list of key-value pairs
    • A graph with two cycles
    • A rooted tree in which each node has at most two children

  5. A tree has 9 nodes, with one root and every other node having exactly one parent. How many edges does it have?

    • 7
    • 8
    • 9
    • 10

  6. A binary search tree is used to store the values 8, 3, 10. Where is the value 3 placed relative to 8?

    • In a separate tree
    • In the left subtree of 8
    • As the root's parent
    • In the right subtree of 8

  7. Which order of traversal of a binary search tree visits the values in ascending order?

    • In-order traversal
    • Post-order traversal
    • Level-order traversal of a queue only
    • Pre-order traversal

  8. A leaf node in a tree is best described as which of these?

    • The root of the tree
    • A node with exactly two parents
    • A node with no children
    • A node that is a cycle

  9. Which is a typical use of a rooted tree?

    • Storing a queue of print jobs in arrival order
    • Representing a file system's folder hierarchy
    • Counting bytes in a binary file
    • Showing a single linear list of numbers

  10. A binary tree has a root with two children and each child has none. What is the height of this tree if the height counts levels?

    • 2
    • 1
    • 3
    • 0

  11. Which statement about trees is correct?

    • A tree does not have to have a root in the general definition
    • A tree must always contain a cycle, which is what separates it from a list of connected nodes
    • A tree always has exactly two children per node, so every node has the same number of links
    • A tree is always directed with one edge per node, joining each node to its single parent

  12. A binary search tree is built by inserting 5, 2, 8, 1. Which node is the right child of 2?

    • 1, which is the right child of 2 because 1 is the last value that was inserted into the tree
    • 8, which is the right child of 2 because 8 is larger than 5 and is placed beneath the root
    • 5, which is the right child of 2 because the root is always the right child of its own children
    • None; 1 is the left child and no right child exists

  13. What is the difference between a parent and a child in a rooted tree?

    • There is no difference
    • A parent is the node directly above, and a child is directly below it
    • A child is above its parent
    • A parent is always a leaf, and a child is always the root

  14. A complete binary search tree with 7 nodes has how many levels?

    • 2
    • 3
    • 7
    • 4

  15. Which description best fits a binary tree node?

    • A value plus references to a parent and a queue
    • A key with a list of weights
    • A single integer with no references
    • A value plus references to at most two child nodes

  16. A graph with a cycle is being checked to see whether it is a tree. What is the result?

    • It is a rooted tree only if the cycle is removed by a root
    • The test cannot be performed on graphs
    • It is not a tree, because trees have no cycles
    • It is a tree because it has a cycle

  17. A tree with 15 nodes is a full binary tree with all levels filled. How many levels does it have?

    • 5
    • 3
    • 4
    • 15

  18. Why is a binary search tree efficient for searching when it is balanced?

    • Each comparison discards about half of the remaining nodes
    • It searches all nodes in order each time, which makes each lookup take as long as the whole tree
    • It stores every value in a single list, so each search reads the values from start to end
    • It requires no comparisons at all, since the position of each value is known from its size

  19. Which term describes the nodes of a tree that have at least one child?

    • Leaves, which are nodes at the bottom of the tree with no children below them
    • Internal nodes
    • Keys, which are the values used to order the nodes and find them within the tree
    • Edges, which are the links that join each node to the nodes that sit beneath it

  20. What does it mean for a binary tree node to have a left child but no right child?

    • The node is a leaf, which means it has no children at all, neither on the left nor the right
    • The node has one child, which is the left one
    • The node is the root of the tree, with no parent and with a single child on its left side
    • The node has two children, one on the left and one on the right, both below it in the tree

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