Yes it's a deadlock, diagram the wait chain of processes (1 -> 2 indicates P1 waiting on P2 to release a resource):
1 -> 3 -> 4 -> 2 -> 1
Ran back into 1 in the wait chain and the cycle is complete; that is 1 is waiting on resources that are waiting on resources that are waiting on 1.
If following 1 like this didn't run back into itself then it would be accurate to say 1 is not in a deadlock (for instance if it was 1->3->4->2). However if one were not in a deadlock that does not prove or indicate none of the others are in dead locks. To verify none of the resources are in a deadlock you would need to graph the same chain with any nodes that weren't in the critical path for 1 (if any in the critical path were in a deadlock then 1 would be, so you know all members of it's dependency chain are not in deadlocks). Since 5 isn't in the critical path you would have to next follow 5's path if 1 wasn't in a deadlock (incidentally 5 is also in a deadlock because it links into the same cycle 1 is in, therefore all listed resources are deadlocked in that cycle)
Another point regarding this particular problem is that all resources available (the set of R1-R5) are already acquired. In such a scenario it is impossible for any process to acquire another resource if no processes are willing to first let go of a resource. A cycle is inevitable in such a scenario. This fact that you should release resources before requesting more is I think supposed to be the lesson of the 73.4 philosophers problem (don't quote me on that)