Nikon D7100 has a 24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor . 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 similarity between these two cameras is that both Nikon D7500 and Nikon D7100 sensors lack anti-alias (Low-Pass) filters. 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 D7100 and D7500 sensor size comparison.
Nikon D7100 and Nikon D7500 have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Nikon D7100 and Nikon D7500 sensors have been tested by DxO and the results show that D7500 has a better overall score of 86, 3 points higher compared to D7100's score of 83.