Which one of the following is not a linear data structure?

A tree is a nonlinear data structure, as opposed to linear data structures such as arrays, linked lists, stacks, and queues. A tree can be empty, with no nodes, or it can be a structure with one root node and zero, one, or more subtrees.

A full binary tree is a binary tree in which each node has exactly zero or two offspring. There are no nodes in a whole tree that have exactly one child.

Hence, option B is the correct answer i.e. Binary Tree.