Samsung NX300 has a 20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor and features DRIMe IV processor. On the other hand, Nikon D7500 has a 21.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor and features Expeed 5 processor.
Another difference between these two cameras is that Nikon D7500's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the NX300 and D7500 sensor size comparison.
Samsung NX300 and Nikon D7500 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.