Both Fujifilm F200EXR and FujiFilm F300EXR have 12.0 MP resolution sensors but Fujifilm F200EXR's sensor is 1/1.6-inch (8 x 6 mm ) and FujiFilm F300EXR's sensor is 1/2-inch (6.4 x 4.8 mm ).
Since Fujifilm F200EXR's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to FujiFilm F300EXR.
Below you can see the F200EXR and F300EXR sensor size comparison.
As seen above, Fujifilm F200EXR has a 1.6x Larger sensor area than FujiFilm F300EXR. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.