Samsung NX100 has a 15.0MP APS-C (23.4 x 15.6 mm ) sized CMOS sensor and features DRIMe Engine processor. On the other hand, Nikon S3500 has a 20.0MP 1/2.3-inch (6.16 x 4.62 mm ) sized CCD sensor .
Nikon S3500's sensor provides 5MP more than Samsung NX100's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the NX100 and S3500 sensor size comparison.
As seen above, Samsung NX100 has a 12.8x Larger sensor area than Nikon S3500. 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.