Which statement correctly describes a binary tree node and its common traversals?

• A. A binary tree node has exactly three children.
• B. A binary tree node has up to two children; traversals include in-order, pre-order, and post-order.
• C. Binary trees are always balanced.
• D. In-order traversal visits right subtree before left.

Answer: (B)

A binary tree node can have up to two children, typically referred to as the left and right child, and the common ways we visit nodes are in-order, pre-order, and post-order traversals. In-order means you visit the left subtree first, then the node, then the right subtree. Pre-order means you visit the node first, then the left subtree, then the right subtree. Post-order means you visit the left subtree, then the right subtree, and finally the node. The statement that a node has exactly three children is incorrect because a binary tree restricts each node to at most two children. Binary trees aren’t required to be balanced, so they can be unbalanced. And in-order does not visit the right subtree before the left; it visits the left subtree first, then the node, then the right subtree.