Which of the following is a type of non-linear data structure?

The correct answer is c) Graph.

A graph is a type of non-linear data structure because it consists of a set of vertices (or nodes) connected by edges, which allows for the representation of relationships between various elements in a more complex manner than linear data structures like queues, stacks, and arrays that organize data in a sequential order. Graphs can have various configurations and can represent relationships in a way that is not strictly hierarchical or sequential.