Sony A7R II has a 42.0MP Full frame (35.9 x 24 mm ) sized BSI-CMOS sensor and features Bionz X processor. On the other hand, Sony A7R has a 36.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor and features Bionz X processor. Sony A7R II's sensor provides 6MP more than Sony A7R'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.
Another similarity between these two cameras is that both Sony A7R and Sony A7R II 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 A7R II and A7R sensor size comparison.
Sony A7R II and Sony A7R have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Sony A7R has 17% larger pixel area (23.83µm2 vs 20.33µm2) compared to Sony A7R II, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.