Is null node equal to leaf node?

No. A null node is a node pointer that holds the null value (zero). A leaf node is simply a node that has no children. Thus in a binary tree, a leaf node would hold two null nodes.

No. A leaf node is a node that has no child nodes. A null node is a node pointer that points to the null address (address zero). Since a leaf node has no children, its child nodes are null nodes.