I am developing a tabbed application.
When I create a new view controller and link it to the tab bar controller, unlike the other two default view controllers, this one
Correct, when you drag a view controller object onto your storyboard in order to create a new scene, it doesn't automatically make the new class for you, too.
Having added a new view controller scene to your storyboard, you then have to:
Create a UIViewController subclass. For example, go to your target's folder in the project navigator panel on the left and then control-click and choose "New File...". Choose a "Cocoa Touch Class":

And then select a unique name for the new view controller subclass:

Specify this new subclass as the base class for the scene you just added to the storyboard.

Now hook up any IBOutlet and IBAction references for this new scene with the new view controller subclass.
To add new ViewController once you have have an existing ViewController, follow below step:
Click on background of Main.storyboard.
Search and select ViewController from object library at the
utility window.
Drag and drop it in background to create a new ViewController.