Is recycle bin a list? And can we query recycle bin to get items deleted from a list,if so how to do it? And also where is the recycle bin data actually stored, is it stored in the content db ?
No, Recyle bin is not a List like other document library and lists. Yes you can Query Recyle Bin item like
All files are internally stored in Content DB in Sharepoint. Once it is Deleted permanently from Sharepoint, they it will be deleted from Content DB.
No it is not a list, it's work on the same concept as we have in windows.
yes you can access it via powershell or other ways. here is powershell example.
In SharePoint everything stored into the Content Database, So all deleted items stored into the Content DB until permanently deleted from recycle bin.