The in-order traversal visits the left child first, then the root, and finally the right child, resulting in 2, 1, 3.

In post-order traversal, the left child is visited first, then the right child, and finally the root, resulting in 2, 3, 1.

The space complexity of a recursive preorder traversal is O(h), where h is the height of the tree due to the call stack.

The worst-case time complexity of inserting an element in a binary search tree is O(n), which occurs when the tree becomes unbalanced.

Level-order traversal is used to print the nodes of a binary tree level by level.