The back portion of model is not visible while rotation If you see in the below image I have pointed the area with red arrows where the surface is not visible. 



I thought that that portion will not have the face so I rotated thee image whenever I am rotating the image it's back surface seems to be invisible. For reference see second image I have pasted.



Can you please suggest why is it so?
That's backface culling on the N panel, on the right side of the viewport, under Shading -> "Backface Culling", this only draws faces which have their normal pointing at the camera, if you deactivate it you turn every polygon "double sided" in the viewport.

For rendering purposes this has no effect, but it might help viewport performance or visibility.