Data structures can be classified as linear or non-linear.
Linear Data Structures: Elements are arranged in a sequential or linear order. Each element has at most one predecessor and one successor.
(A) Array: Elements are stored in contiguous memory locations, forming a sequence. It is a linear structure.
(B) Stack: A list of elements where insertion and deletion occur at one end. Logically, it's a linear sequence.
(C) Queue: A list of elements where insertion occurs at one end and deletion at the other. Logically, it's a linear sequence.
Non-Linear Data Structures: Elements are not arranged sequentially. An element can be connected to multiple other elements.
(D) Tree: A hierarchical structure where elements (nodes) are connected in a parent-child relationship. A node can have multiple children, so the structure is non-linear. Graphs are another example of non-linear structures.
Therefore, a Tree is not a linear data structure.