Both Sony HX350 and Nikon B700 have 20.0 MP resolution sensors but Sony HX350's sensor is (1/2. ) and Nikon B700's sensor is 1/2.3 (6.17 x 4.55 mm ).
Since Nikon B700'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 Sony HX350.
Below you can see the HX350 and B700 sensor size comparison.
As seen above, Nikon B700 has a infx Larger sensor area than Sony HX350. 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.