can we have stories in sprint without assignee

When sprint starts, is it mandatory to have all the stories that are part of the sprint should be assigned to a resource?

Naveen Hks, In my opinion, No, the PBI's are converted to a Done Increment by the Development Team. How they decide to accomplish this as a "team" is upto them. This is how they self-organize.

There are a few things to keep in mind:

• Scrum does not require "stories". Although User Stories are a common representation for Product Backlog Items, they are not the only way. Even if User Stories are used for some Product Backlog Items, some work may not be best suited to this style and alternative formats are used.
• Scrum does not require assigning Product Backlog Items or Sprint Backlog Items to anyone at any point in time. Some teams may find this useful to understand who is the primary person working on something. Some teams may assign to a group instead, such as a pair. Sometimes, tools may enforce that a person is assigned to each work item. None of this comes from Scrum, though.
• It's best to not refer to people as "resources". People are people. When you refer to people as resources, you often start to see them as more interchangeable than they really are. People have unique backgrounds, knowledge, and skill sets that allow them to contribute to the team and organization.

I have a basic question. When sprint starts, is it mandatory to have all the stories that are part of the sprint should be assigned to a resource?

When a Sprint starts, it might be reasonable to then start Sprint Planning. What does the Scrum Guide say about this event? What conclusions can you draw about "stories", the "assignation" of work to so-called "resources", and what is and is not "mandatory"?

Scrum has nothing to say about stories or how they are used. 

Practically, in my teams the story is never assigned to a single person because the team owns these. The tasks we do have an "assignee" but it's just designating the team member who picked up that individual task; no one is directing the team to take a particular task.