It has an "F" lens mount. source: http://www.dpreview.com/reviews/nikond50/page5.asp

It's A-mount.

It depends on the make of the lens and the mount type. Newer Canon lenses have an EF mount while Nikon lenses have a Nikkor mount. Though you can purchase conversion kits to put a Canon lens on a Nikon and vice versa.

No, this is a point & shoot camera and there is no lens mount. The lens is fixed on the camera and cannot be removed.

Nikon F mount (with AF coupling and AF contacts)