What is a complete binary tree?

(a) Each node has exactly zero or two children

(b) A binary tree, which is completely filled, with the possible exception of the bottom level, which is filled from right to left

(c) A binary tree, which is completely filled, with the possible exception of the bottom level, which is filled from left to right

(d) A tree In which all nodes have degree 2

The query is from Binary Tree Properties in division Binary Trees of Data Structures & Algorithms I

I had been asked this question by my school principal while I was bunking the class.

The correct answer is (c) A binary tree, which is completely filled, with the possible exception of the bottom level, which is filled from left to right

Explanation: A binary tree, which is completely filled, with the possible exception of the bottom level, which is filled from left to right is called complete binary tree. A Tree in which each node has exactly zero or two children is called full binary tree. A Tree in which the degree of each node is 2 except leaf nodes is called perfect binary tree.