What is the output of below algorithms on a disconnected Graph? If I apply Dijkstra's ,BFS or Bellman-ford algorithm on a disconnected Graph then will the output be a tree or a disconnected Graph only because even if we have a disconnected Graph and we run Dijkstra's algorithm on it then it will return shortest path in the connected component only , but we maintain a predecessor array in all the algorithms which has information about the parent from which the node learnt the path so it will values for all the vertices , so even if we have a disconnected Graph then still other vertices will also be printed .

So output is Graph right for all the algorithms whether the graph is undirected or directed ?
No.  The output of Dikstra's algorithm is a set of distances to each node.  It's not a graph or a tree.  This is true no matter whether the input graph is connected or disconnected.  The standard algorithm for Dijkstra's algorithm sets the distance correctly for all vertices in all components (not just the ones in the same connected component as the source).  The standard algorithm doesn't print anything, so if you are printing something, you're probably adding something extra to the standard algorithm, and we can't analyze that without seeing what your variation of the algorithm is.