Final answer:
The process that an ArcGIS user should perform to visually enhance a dark and grainy raster dataset is contrast stretching, which expands the brightness range to increase visual distinction.
Step-by-step explanation:
To visually enhance the appearance of a raster dataset that appears dark and grainy in ArcGIS, the appropriate process to perform is A. contrast stretch. Contrast stretching improves the raster's visualization by expanding the range of brightness values, thereby using the full range of possible values to increase visual distinction between features. This process enhances the dark and light tones while maintaining the overall balance of the image. Adjusting transparency and increasing brightness might offer some improvement to visibility, but it wouldn't address the graininess. Modification of the RGB composite is typically used for adjusting color, not contrast or graininess.