Sony RX1R II has a 42.0MP Full frame (35.9 x 24 mm ) sized BSI-CMOS sensor and features BIONZ X processor. You can shoot at maximum resolution of 7952 x 5304 pixels with aspect ratios of 1:1, 4:3, 3:2 and 16:9. RX1R II has a native ISO range of 50 - 25600 which can be boosted to 102400 and it can save files in RAW format which gives you a wider room for post processing.
Sony RX1R II is not the highest resolution Full frame camera. Sony A7R IV with its 61.0MP sensor is leading in this class. Check the comparison of Sony RX1R II vs Sony A7R IV or take a look at Highest resolution Compact cameras list.
Sony RX1R II DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. Sony RX1R II sensor has been tested by DxO Mark and got an overall score of 97 for its image quality. You can find the details of their analysis of Sony RX1R II here.
Another important feature about Sony RX1R II's sensor is the lack of anti-alias (Low-pass) filter. Removing anti-aliasing filter increases the sharpness and level of detail but on the other side it also increases the chance of moire occurring in certain scenes. But wait! RX1R II takes care of this problem for you. It has a unique and adjustable Anti-Aliasing Filter Simulator mode which can create the effects of a Low Pass filter electronically when you want to avoid moire.
Let's look at how the size of the Sony RX1R II's Full frame sensor compares with other standard sensor sizes.