Both Nikon B500 and Pentax X-5 have 16.0 MP resolution sensors but Nikon B500's sensor is 1/2.3 (6.17 x 4.55 mm ) and Pentax X-5's sensor is 1/2.3-inch (6.08 x 4.56 mm ).
Since Nikon B500'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 Pentax X-5.
Below you can see the B500 and X-5 sensor size comparison.
Nikon B500 and Pentax X-5 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.