Which of the following data structure is useful in traversing a given graph by breadth first search?a)Stackb)Queuec)None of the mentionedd)List

The correct answer is b) Queue.

Here's why:

Breadth-first search (BFS) is an algorithm for traversing or searching tree or graph data structures. It starts at the tree root (or some arbitrary node of a graph, sometimes referred to as a 'search key') and explores the neighbor nodes at the present depth prior to moving on to nodes at the next depth level.

The BFS algorithm uses a queue data structure to keep track of the nodes that it needs to visit. Here's a step-by-step explanation:

1. Start by putting any one of the graph's vertices on the back of a queue.
2. Take the front item of the queue and add it to the visited list.
3. Create a list of that vertex's adjacent nodes. Add the ones which aren't in the visited list to the back of the queue.
4. Keep repeating steps 2 and 3 until the queue is empty.

So, the queue data structure is useful in traversing a given graph by breadth-first search.